We have had excellent results with the Garmin Rino 650. The radio broadcasts your location to all the other radios, and is able to poll the location of other radios passively, and navigate a user to other radios.
If I want to find someone, I just poll their location, the radio will show me which direction they are in and how far, and I start walking. Eventually, I will simply run into them.
The only con is the price.