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I'm sorry to hear about your brother, I've personally never been in that situation before, so I'm not sure on the advice.
Personally, the closest I've come to is my boyfriend was kidnapped when he was about 11. He was gone for a week, and they found him because a schoolmate of his happened to notice the exact color, make, and model of the truck that took him from his bus stop.
In the end, they found him and another boy that had been missing for about 4 years. My boyfriend was all over the news and his mom was even on usa today and Oprah (I'm not 100% about Oprah lol)
edit: just googled it and yeah they were on Oprah. xD
anyways, enough about me/him. I know I tear up anytime I think about it happening, but I promise if you guys keep at it, there will be a break through, just like there was for my bf. Someone, at least one person, knows something. Just gotta be persitant on finding that person. I wish you and your family the best in finding him.