like someone mentioned, not everyone checks and responds to messages in their inboxes.
maybe he didn't respond to your message because he felt it crossed a boundary (something which you didn't know )
maybe someone else said something which crossed a boundary and he left the site for a while
maybe he just had a life and was too busy to hit the site (it happens..things pile up and you don't go to the computer)

leave it. in time he'll check the box or not.

see him on line post something like good to see you. if it sparks interest good...