Just stumbled upon this forum, no idea if this could help.
About 10 years ago in high school we had a foreign exchange student, Yuhei Yoshida, who we very quickly lost contact with when he went back to Japan. From what I can remember, he had a brother named Shuhei (not sure on the spelling. I don't even know where to begin the search for relevant information. Is hiring a Japanese private detective an option?
Attached is a picture of us at the airport right before he returned to Japan. He was supposed to stay for the summer, but a strange series of events unfolded and his host family made him go back sooner than expected.
His facebook has been dead since pretty much right after he left, and I can't find a trace of him on any other social media popular in America currently.
Any info or places to start looking would be helpful!