my friend

Hello, I'm writing on behalf of a friend. She Gave up a little baby girl for adoption in 1968 (at age 16). Her reason's... I think mostly pressure from her family, her young age.... after all she was a 16 year old unwed mother. She contacted some sort of private investigator person, that gave her a whole bunch of half information. ie. let her look at a copy of the birth certificate... gave her a bunch of names and addresses of people who might be her daughter. clamed to know the adoption case number and date of adoption. Aparently (according to the private investigator) the child was adopted at age 1 1/2.) . My friend would like to locate and meet with her birth daughter (if possible). How do we start that process? what are we facing? What are the chances that we will actually find her? thankyou