If you know where he's at, just drop an email and say "Hey, this is _____. We used to be good friends back (whenever it was). Do you remember me? I was just thinking about you and wondered how you were doing." If they remember you then rehash some old memories you have of them and hopefully the conversation will flow in the right direction - unless if they are the opposite sex and they are now married then I'd leave it alone.
_________________
Me grumpy?
I'm happiness challenged.
Your neurodiverse (Aspie) score: 83 of 200
Your neurotypical (non-autistic) score: 153 of 200 You are very likely neurotypical
Darn, I flunked.