June 4th, actually, according to his profile. That's about two months missing. And it appears that he hasn't updated his trading list since then, either.
I assume you've tried e-mailing him? It seems sorta odd... not sure what's going on. There's probably some justifiable reason for this, though what it is, I don't know.
If you're not able to get ahold of him via e-mail, you could try sending him something via actual mail... since he got your cards, snail mail apparently works, if nothing else.
I dunno, man. Weird that he just up and disappeared. I wonder what (if anything) happened....