A social networking system identifies a set of groups of which a user of the social networking system is not a member and selects a group for recommendation to the user based on a predicted affinity of the user for each identified group. The social networking system computes an affinity score of the user for each of one or more members of the selected group based at least in part on information describing a set of connections between the user and each member. Based on the scores, the social networking system selects a set of members of the group and generates a recommendation unit, wherein images associated with the selected members are arranged based on their scores and overlay at least a portion of an image associated with the group. The recommendation unit is communicated to the user to suggest that the user join the recommended group.