Unknown sibling?

Hey, so I have a few questions and figured I’d ask them here. So...my mother and I were talking the other day, and she said that when her and my dad first got together, an ex girlfriend of his claimed she was pregnant. He didn’t believe her, so he let it go. She said she believed the girl, but my dad didn’t so there was nothing she could do about it. Well, I’d kind of like to find out if I have a sibling out there somewhere. I have no plans of busting into this persons life. But if they’re trying to find out about their bio dad, I’d like to help. Medical issues run wild on that side of the family as well. I don’t even know where to begin trying to find them. I only want to contact him/her if they’re actually looking for his/her father. My father passed away about 10 years ago, so I can’t ask him anything about this. Where are some places to look and see if they’re searching? Sorry if this doesn’t make sense, just something that’s been on my mind and don’t really know how to put into words.