For example, the user list generation server identifies an additional set of user identifiers for an additional set of users that are in a same user group (e.g., same user interest group) as at least one user in the original set of users in 306. As mentioned in reference to the process 200 in FIG. 2, the original set of user identifiers can include all users that perform actions on an electronic resource of an entity (e.g. a publisher or digital component provider). Some of these users can further be grouped into groupings, clusters, or cohorts based on the resources visited by the users (e.g., user interest groups). For example, a portion of the users in the original set of users can be grouped together based on purchasing or otherwise clicking on clothing. Another portion of the users in the original set of users can be grouped together based on clicking on gardening equipment. Here, in 306, the user list generation server can determine whether any users are also grouped into the cluster for clothing and/or the cluster for gardening equipment—in other words, the user list generation server can determine whether any of the users are in the same user interest group. If those users are in either cluster, those users can be identified in the additional set of user identifiers. These users can then be added to the user list (e.g., the user action group) in order to expand the user list.
