@ariana17,
Ask your mother questions, such as how old she thinks he is/was, does she know things like where he was at school or work, whether he has any siblings, his hometown, his birthdate, his religion, that sort of thing.
Keep in mind that she may not want to talk about him in detail. Ask if any of her friends knew him, too.
Also keep in mind that he is a deadbeat. He never took care of you. The likelihood is high that he was married when you were conceived, or he could be a different faith (with disapproving parents). He could be in jail or dead for all you know.
Please don't construct a fantasy about this man who has never supported you and may not know you exist.