would suggest you to ask around the irc, maybe he just changed nick but still online somewhere.
usually one's habits are not changed so easy, so if he used to be in irc, most chances he still there, somewhere at least. ;)
also, consider indeed he might not want u to contact him

(as harsh as it may sound).
as i'm sure someone from that forum admins already pm'ed him about it, as usually it's makes no sense for admins & mods not to mention this to him, as most admins do want to help.
last thing u can do to to eliminate the above speculation, is just to post message on the forum, asking him to contact you, and leave your email there. i'm sure he will see it, and if he is indeed your friend he will contact you back.