Lizbud ~ Thank you for doing all of this for that poor baby. He sounds like a great, socialized kitty. I best someone is really missing him. Your vet can scan him for a microchip. You can take a photo of him to the shelters and fill out a "found cat" form. That way if the owners are desperately searching for him, they may have half a chance of finding him. Unless the shelter is a "no kill", I'd advise against taking him there.
Also, ask kids in the neighborhood if they know where the cat lives. That's how we found out that Kuhio was at the shelter. We were too late to save her.