[ice]

Go into the iTunes app then the music tab the persons email address will be right at the bottom of the page then send them an email

You can also contact apple, if they registered for the apple protection plan they will have the info, apple would have a better chance at tracking then a service provider, you can also see on facebook if the persons address/home phone is listed. And you could go into the photo roll, then places and If you see an Adress with an accumulation of photos you could take it their,
If iCloud is not enabled enable it so the owner can track the phone with the find my iPhone app.