Any number of mobile devices each execute an application allowing them to subscribe to a group. Alternatively, the devices subscribe at a Web server. A percentage of the group and a distance threshold from a target device are defined. Each device sends its GPS data to a Web server or to one of the designated mobile devices. Alternatively, the target device calculates its distance to the other devices using wireless signals. The designated device or the Web server calculates the distance from the target device to the other devices. If the distance is over the threshold then an alert is generated and sent from the Web server to designated recipients, or sent from the designated device to the recipients. Distance from the target device to the group members may be calculated based upon a majority, a percentage of the group, or a special cluster of the group.