Vehicular networks have attracted significant attention in the context of traffic control and management applications. However, vehicular networks also have important applications in crime prevention and criminal investigations. This paper presents a system for passively tracking a target vehicle whose driver is assumed to be a "person of interest." The tracking system relies on the dynamic recruitment of neighboring vehicles of the target as agents. A mobility prediction algorithm is used to probabilistically predict the target's future movement and to adjust the tracking process. Combining agent-based tracking and mobility prediction enables a target vehicle to be passively localized and tracked in an efficient manner.