I came here hoping for a happy update. I'm sorry. I still feel confident he will turn up either at a shelter (and think back to when he was chipped, and make sure you haven't had a change in contact info since then), or you will find him in a neighbors yard, hiding. I have tracked down several cats that hadn't traveled more than a few hundred feet, by spotting their eye shine at night. The little effers didn't make a peep, or come out when called numerous times, when they were clearly right there and could hear me calling. If I weren't so relived to see them I'd strangle them.
We've had 4 family cats (mine, parents or grandparents) that we've had to track down, and found all 4. One took a long time though, and was gone for over a year. At the one year mark, my grandparents finally gave up and said "he's not going to be found, lets go to the shelter and get another cat".
I took them to the shelter, and guess who was in one of the cages. I was a bit miffed, since I'd called that shelter daily for a while, then weekly, and still had been calling monthly looking for that cat. He'd been there nearly the whole time, but they had him mislabeled as a girl.
Don't give up.