Looking for Sabrina

So a couple days ago Dh tells me he wants to try and find his daughter.  He hasn't seen her since she was about a year old, and that was a good 18 years ago.  Her first name is Sabrina, but she has her Mom's last name and he doesn't know what that is.  Dh's cousin probably knows what it is but I haven't been able to get ahold of him yet.  How do you look for a child and what does he say if we do find her? It's been a long time.  She probably doesn't even know about him since her Mom ran off with her and never looked back. He has a picture of her, from when she was about 3 years old.  I'm not sure where it came from but I know he treasures it.