How can I find a friends bank account?

[German]

The question seemed weird, I know. It's not what seems though.
My friend is an E-6 in the Marine Corps but he recently moved to Virginia to start working there, and possibly get a W-2, or EO-2 as some may know it, rank.
He let me borrow $40 but he left before I could give him the money, and my old phone got damaged before I could save his number. He also doesn't have a Facebook account or anything via the social network.
I know his full name, and I think he has Navy Federal but, I could be wrong.
How can I find his bank account without the/a bank thinking I'm some sort of thief?