How do you find a lost sibling (or other relative)?

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I have a friend who called me today and she was very upset over the phone so I went to see her. I thought she was having a problem with her boyfriend and since she is pregnant and emotional I figured she just needed a little cheering up and encouragement. I was not prepared to hear what I did......I knew she had not seen her younger brother in years because they were both put in foster care due to abuse. She is now 20 and since I have known her (which has only been a couple of months) she has mentioned a few times that she wonders how her brother is doing. Right now her mother is in a psychiatric hospital because she has been so messed up by the long term abusive relationship. What happened today was her mother called her because she did not hear from her yesterday (Mother's Day). They don't talk much anyway. During the conversation her mother told her that her brother was dead....that he had been kidnapped out of foster care a few years ago by the abusive father and killed in the woods. Please know that part of her instability is that she says inappropriate things all the time, but this girl is devastated to even think it may be remotely true and so I would like to help her try and find her brother (or at least find out if he's been declared as deceased). Can anyoen advise me on where to start this search? Thanks.