Looking For My Lost Half Brother?

Somewhere in the world I have a half brother that I have never met, and the sad part is that my dad hasn't either. My dad had a girlfriend in Mexico which he brought her to the U.S. They lived in PHX, AZ for a while. Before my dad brought her, the "girl's" mom told my dad if things don't work out please bring her back. Things did not work out with her and my dad so my dad decided to bring her back to mexico like he had promised her mom. My dad told me that before he left her, back at their apartment where they used to live she would serve herself mive amounts of food and then when she was going to sit down and eat she would get nauseous and obviously run to the bathroom and vomit. (I mean I don't understand why it did not cross my dads mind that she could of been pregnant.) Anyway, he took her back to Mexico and left her. A couple of months later he went back to the same place her met and left this girl at. He went to a bar and ask this guy that knew this girl that if he knew anything about Mari (the girl my dad had took.) The guy then went on to tell my dad that she had gave birth to a little boy. The worst part was that she gave the baby up to some Americans in exchange to pay for her hospital bill. When my dad found out that he had this son it was too late because she had already sold him. My question is... if there is anyway that I can try to look for him. My dad told me that most likely the Americans that paid for him are probably living in Sierra Vista, AZ. The more I think of it... I feel like it's impossible. Help:(