In one embodiment, a method comprises receiving, via a first portable electronic device, contextual information and a geolocation relating to a first user in a network-based system and receiving, via a second portable electronic device, contextual information and a geolocation relating to a second user in the network-based system. A common element in the received contextual information relating to the first and second users is identified.In response to an identification of the common element, a boundary for a geofence is defined based on the geolocation of the first or second user. The geolocation of the first or second user is automatically monitored and the boundary of the geofence is dynamically adjusted based on the identified common element and a change in the geolocation of the first or second user. In one example, the boundary of the geofence is redefined to exclude at least one member from a population of the geofence.