Ive been on ancestry.com and a relative was saying her twin sister got stolen at birth, what agencies help find people like that, she's hoping her sister gets on ancestry so she can find her that way.
Maybe ancestry.com would work if both sisters are looking for each other but if they aren't a Private detective might be able to help. Also a private detective could tell the other person what her twin is like - she could be crazy and out for revenge because she grew up being told that her real parents left her in a parking lot because they didn't want to take care of her or something like that. Cheers and happy weekend!
If they both completed a DNA kit from the same company, maybe. 23andMe shows a list of your DNA relatives, and how close they are related to you.
Ancestry.com likely wouldn't work. I mean, it's doubtful the people who stole one child would tell that child the truth about who her real parents were. So there would be no genealogy link for her to find relatives.