My adoption was private. Speaking about adoptive the adoptive family here... My Aunt's FIL was a Dr. in Pennsylvania and new my parents were looking to adopt. I have the court transcripts and all other records dealing with the adoption. I even have two birth certificates.
My biological family's last name is unique and they are the only family in the US with that name. With the advent of the Internet, typing in the last name does yield answers.
Death records... And they all pointed to Pennsylvania. About ten years ago, I found a post in a genealogical website. A cousin was trying to track down any other family members and was trying to put together a family tree. I kept in contact with her and a couple other relatives for a while, but fell out of contact. Then after a few bored nights on FB, I searched and found them again. I have been communicating with one of my Aunts, but have reconnected with the cousin and another.