Not sure if this is feasible to create without the players themselves leaving some form of tracks. In reality it's still very possible to cover up all your tracks after all. So how would one distinguish from that/be able to cover their tracks?
First, I frankly doubt it would be feasible without draining server resources.
Regarding a system, for brainstorm purposes, I'd say:
The player tracking tags the player he wants to track (for you need to know who you're looking for or receiving dm indication if who was in that scene). After that, the tracking player rolls consistently for search x the tagged player MS (with a bonus if the player is in stealth). A success means you jeep the trail,a failur you lost it.