From time to time I need to track "lost" devices used by employees. But I'm always disappointed that, AFAIK, no single app has all the features basic features:
Remotely activate GPS on the "lost" device. Androidlost and Airdroid does this well.
Frequent updates with heading and speed. (Low bandwidth protocol like UDP ??) And while the GPS is waiting for a lock, display the satellite reception strengths.
Support both phones and tablets.
Easy to use authentication, like Airdroid.
Easily allow groups to track each other. Just like adding people to a hangout.
Chase the "lost" device with another android. On reflection, the simpler the better. Distance and bearing is enough: http://xkcd.com/407/