The invention claimed is:1. A method comprising:receiving, by a content platform and from a client device of a user, a request for a digital component, wherein the request includes a user identifier that uniquely identifies the user to the content platform;determining that the user identifier is included in a user list that includes a plurality of user identifiers respectively corresponding to a plurality of users in a user action group, the plurality of user identifiers comprising (i) a first set of user identifiers for a first set of users that performed one or more particular actions at an electronic resource of an entity for which the user list is generated and (ii) a second set of user identifiers for a second set of users that have been added to the user list based at least in part on each user in the second set of users being in a same user interest group of a plurality of user interest groups as at least one user in the first set of users, wherein each user interest group in the plurality of user interest groups includes users that have been assigned to the user interest group by applications running on devices of the users based at least in part on electronic resources visited by the users;in response to determining that the unique identifier is included in the user list, selecting a digital component of the entity for which the user list is generated; andproviding, to the client device of the user, the digital component for display to the user of the client device.2. The method of claim 1, further comprising:identifying a third set of users that are in the same user interest group as at least one user in the first set of users; andgenerating an intermediate user list with the third set of users.3. The method of claim 2, further comprising:identifying, for each user in the third set of users, a geographic identifier that indicates a geographic location of the user; andselecting, for inclusion in the second set of users, each user in the third set of users for which the geographic identifier satisfies a location condition for the user list.4. The method of claim 2, further comprising:identifying, for each user in the third set of users, a level of online activity of the user;ranking the third set of users in the intermediate list based on the level of online activity of each user in the third set of users; andselecting, for inclusion in the second set of users, a proper subset of the third set of users based on the ranking.5. The method of claim 4, wherein the level of online activity for each user is measured in a predefined time period ending at a time at which the user list is generated.6. The method of claim 2, further comprising:identifying, for each user in the third set of users, user embeddings that indicate user preferences of the user;ranking the third set of users in the intermediate list based on the user embeddings for each user in the third set of users; andselecting, for inclusion in the second set of users, a proper subset of the third set of users based on the ranking.7. The method of claim 2, further comprising:generating, for each user in the third set of users, a score based on a set of data comprising (i) the user identifier associated with the user, (ii) the user interest group, (iii) an entity group of the entity, (iv) electronic resources of the entity, and (v) keywords associated with the entity; andselecting, for inclusion in the second set of users, each user having a score that satisfies a threshold score condition for the user list.8. The method of claim 7, wherein generating, for each user in the third set of users, a score comprises:receiving the set of data;providing the set of data as input to a machine learning model that was trained to correlate training sets of data with likelihood of a user performing one or more specified actions to determine first and second arrays, wherein the first array corresponds to a user embedding associated with the user and the second array corresponds to an entity embedding associated with the entity;determining a distance between the first array and the second array; andassigning the score for the user based on the determined distance between the first array and the second array.9. The method of claim 8, further comprising:ranking the third set of users in the intermediate list based on the assigned score for each user in the third set of users; andselecting, for inclusion in the second set of users, each user from the ranked intermediate list having the assigned score that exceeds the threshold score condition for the user list.10. The method of claim 8, wherein the machine learning model is a deep neural network (DNN).11. A system comprising:one or more processors; andone or more storage devices storing instructions that, when executed by the one or more processors, cause the one or more processor to perform operations comprising:receiving, by a content platform and from a client device of a user, a request for a digital component, wherein the request includes a user identifier that uniquely identifies the user to the content platform;determining that the user identifier is included in a user list that includes a plurality of user identifiers respectively corresponding to a plurality of users in a user action group, the plurality of user identifiers comprising (i) a first set of user identifiers for a first set of users that performed one or more particular actions at an electronic resource of an entity for which the user list is generated and (ii) a second set of user identifiers for a second set of users that have been added to the user list based at least in part on each user in the second set of users being in a same user interest group of a plurality of user interest groups as at least one user in the first set of users, wherein each user interest group in the plurality of user interest groups includes users that have been assigned to the user interest group by applications running on devices of the users based at least in part on electronic resources visited by the users;in response to determining that the unique identifier is included in the user list, selecting a digital component of the entity for which the user list is generated; andproviding, to the client device of the user, the digital component for display to the user of the client device.12. The system of claim 11, wherein the operations comprise:identifying a third set of users that are in the same user interest group as at least one user in the first set of users; andgenerating an intermediate user list with the third set of users.13. The system of claim 12, wherein operations comprise:identifying, for each user in the third set of users, a geographic identifier that indicates a geographic location of the user; andselecting, for inclusion in the second set of users, each user in the third set of users for which the geographic identifier satisfies a location condition for the user list.14. The system of claim 12, wherein the operations comprise:identifying, for each user in the third set of users, a level of online activity of the user;ranking the third set of users in the intermediate list based on the level of online activity of each user in the third set of users; andselecting, for inclusion in the second set of users, a proper subset of the third set of users based on the ranking.15. The system of claim 12, wherein the operations comprise:identifying, for each user in the third set of users, user embeddings that indicate user preferences of the user;ranking the third set of users in the intermediate list based on the user embeddings for each user in the third set of users; andselecting, for inclusion in the second set of users, a proper subset of the third set of users based on the ranking.16. A computer readable storage medium carrying instructions that, when executed by one or more processors, cause the one or more processors to perform operations comprising:receiving, by a content platform and from a client device of a user, a request for a digital component, wherein the request includes a user identifier that uniquely identifies the user to the content platform;determining that the user identifier is included in a user list that includes a plurality of user identifiers respectively corresponding to a plurality of users in a user action group, the plurality of user identifiers comprising (i) a first set of user identifiers for a first set of users that performed one or more particular actions at an electronic resource of an entity for which the user list is generated and (ii) a second set of user identifiers for a second set of users that have been added to the user list based at least in part on each user in the second set of users being in a same user interest group of a plurality of user interest groups as at least one user in the first set of users, wherein each user interest group in the plurality of user interest groups includes users that have been assigned to the user interest group by applications running on devices of the users based at least in part on electronic resources visited by the users;in response to determining that the unique identifier is included in the user list, selecting a digital component of the entity for which the user list is generated; andproviding, to the client device of the user, the digital component for display to the user of the client device.17. The computer readable storage medium of claim 16, wherein to the operations comprise:identifying a third set of users that are in the same user interest group as at least one user in the first set of users; andgenerating an intermediate user list with the third set of users.18. The computer readable storage medium of claim 17, wherein the operations comprise:identifying, for each user in the third set of users, a geographic identifier that indicates a geographic location of the user; andselecting, for inclusion in the second set of users, each user in the third set of users for which the geographic identifier satisfies a location condition for the user list.19. The computer readable storage medium of claim 17, wherein the operations comprise:identifying, for each user in the third set of users, a level of online activity of the user;ranking the third set of users in the intermediate list based on the level of online activity of each user in the third set of users; andselecting, for inclusion in the second set of users, a proper subset of the third set of users based on the ranking.20. The computer readable storage medium of claim 17, wherein the operations comprise:identifying, for each user in the third set of users, user embeddings that indicate user preferences of the user;ranking the third set of users in the intermediate list based on the user embeddings for each user in the third set of users; andselecting, for inclusion in the second set of users, a proper subset of the third set of users based on the ranking.