That makes it slightly harder...although there's a way you could go about locating him.
If you know he's online, you can try whisper him in the whisper chat window on a toon you won't use. If the whisper goes through, he's on that side. If it doesn't, he's not (OR he could be busy porting from one area to another - that usually doesn't take more than 5 to 40 seconds, depending on his computer and connection - OR he could be on a different toon).
To whisper, hit Enter to bring up the chat window in the lower left corner, then select Whisper and type in his name exactly as it is spelled and then just a letter or something. The content of the chat window should look something like this (spaces included) for whispers:
! nameofplayer message