Here are, I believe, the two most likely possibilities:
1) he's dead.
2) he doesn't want to be found
Occam's Razor makes short work of any other explanation I can think of.
It is possible that he may still be here under some other name. If so, odds are pretty high he's reading this thread. If this were the case, he would identify himself unless he specifically wanted to remain unknown.
For this reason, I hope that if anybody DOES find anything out about him, they'll take it directly to Dave rather than posting it publicly. If he is still out there and does not wish to be discovered, he no doubt has is reasons, and we should respect that.
That said, I think the only way we could really find him would be to start with information (such as IP addresses) that only Dave currently has access to. Do we still have records showing where Gray posted from? If so, that would be the place to start.