My iPhone was returned anonymously to me yesterday. How can I find/reward the person?

I lost my phone yesterday in a parking lot, and the young man who found it after I had gone called three people in my contacts list to track me down. He then went to the trouble of driving to a bookstore and leaving it there, anonymously, for my friend, who is returning it to me tomorrow. The finder would only say on the phone that he was a college student and wished he could afford such a nice phone. He wouldn’t give his name or number to my friend. It’s probably a hopeless cause finding this honest young man, but I so much want to thank and reward him. Any ideas I’m overlooking?