I don't have an idea where he is.. Maybe he's busy with his girlfriend or whatever it is... Try to email him or im him if you have his email or yahoo screenname or aim screenname?
I'm sure AJ is just taking a little break from AD for a while. I recently took a break from AD for about two weeks but I'm back. I'm sure AJ will be back whenever he feels like to.
I will let AJ know that he's being missed in AD. Usually when weather is nice and warm/hot, he's outside more. I still talk to him occassionally online.