An online system identifies a group of users of the online system based on connections between the users of the group maintained by the online system and distances between the users during a particular time interval. The online system predicts a purpose of the group and one or more common interests shared by users of the group. The predicted purpose and common interest(s) are mapped to content items eligible to be presented to one or more users of the group. A confidence score and/or bid price is computed for each content item to which the purpose and common interest(s) of the group are mapped. The online system selects one or more content items for presentation to one or more users of the group based on the confidence scores/bid prices.