I am searching for my birth family?

If anyone can tell me how to find these people, please help. My birthmother's married name is Barbara Kramer, her birthdate is 9-22-46. I was born in Pittsburgh, so I am uming she was born in that area as well. She married Leo Kramer when she was 17, and they had four children: Leo Kramer Jr, who was born 8-31-65, Brian Kramer, who was born 10-21-66, Donna Kramer, who was born 4-14-68, and Steven Kramer, born 6-7-71. Barbara and Leo divorced in 1972. I am desperate to find either my birth mother, or my siblings, and the agency that handled my adoption will not ist me. I am uming they are in the PA area... Can anyone help?