1. A method comprising: receiving, via a first portable electronic device, contextual information and a geolocation relating to a first user in a network-based system; receiving, via a second portable electronic device, contextual information and a geolocation relating to a second user in the network-based system; identifying a common element in the received contextual information relating to the first user, and the received contextual information relating to the second user, wherein the common element is not pre-identified and is identified upon a comparison of the first and second contextual information; in response to an identification of the common element, defining a boundary for a geofence based on the geolocation of the first or second users; automatically monitoring the geolocation of the first or second user; dynamically adjusting the boundary of the geofence based on the identified common element and a change in the geolocation of the first or second user; and redefining the boundary of the geofence to exclude at least one member from a population of the geofence, the exclusion based on an identified change in geolocation or contextual information relating to the at least one excluded member.