There's this app
Plan B, which you can install from Google's market (Play) that sends you emails regarding the location of the phone. But its done "after" the phone is lost.
And of course, it would only work if data is on 24 x 7. Read the description carefully. But I don't vouch on this app much though.
Preventing it from getting stolen is the best choice.
*play.google.com/store/apps/details?id=com.lookout.labs.planb