A system and method for tracking crowds of users are provided. In one embodiment, a central system, which includes one or more servers, operates to obtain current locations for users of mobile devices. Based on the current locations of the users, the central system forms crowds of users. As a result of movement of the users and corresponding location updates, the crowds move and change over time. In order to track at least some of the crowds, crowd snapshots for those crowds are created over time and stored. The crowd snapshots preferably maintain anonymity of the users in the crowd at the time the crowd snapshots are created. Thereafter, the crowd snapshots may be used to generate crowd tracking data for select crowds.