When I was a kid my mum had a queen with a litter and found a home for two of the kittens with a couple from a nearby city (so I expect they were kept indoors.) When the kittens were 18 months the wife called and ask if we could take them back- she was pregnant, her husband in the navy and she was worried about what they might "do" to the baby.
Mum stopped herself letting the woman know what she thought of her and agreed to have them back. They were kept indoors for a while, but as my mum always had a LOT of cats which were allowed to roam, at one point they got out and as mum said "got the wind up their tails" and ran.
Luckily they were neutered and we lived in a very rural location so there was little worry about them coming to harm in the usual ways, but we still worried about farmers setting illegal traps and poison ... They had run far and wide and despite all the daily walks around, calling, notices we put up and enquiries we made, for 3 months we found nothing.
Word of mouth got around, we had a couple of sightings so we borrowed a couple of RSPCA cat traps and left them in the places we'd been told about. And one of the cats, PC Plod the huge silver tabby, was found!
It took a further 9 months to find Possum, his sister, but eventually we got her the same way, and in the meantime we found a black feral cat (Rameses - we worked out she was a girl not a neutered tom later) with a horribly tight collar (must've been dumped as a kitten) who came back with us too.
They all settled in (even Rameses - who was a character to say the least but eventually started trusting us, stopped scratching and just hogged the electric fire and kept the other big cats in their place instead) and all three lived really happily with my mum to grand old ages and never ran away again.

So hey - you don't have to lose hope. Why not post on the internet! A girl just found her lost husky in London after setting up a facebook group. Cats are incredibly capable and can look after themselves, even through a winter on the moors, as we found out. In the countryside there's great hunting to be had, and in the city they can scavenge untold titbits and have every chance of being picked up by someone and taken home.

Really hope that you find him one day (he's a beautiful boy)- and if you don't... - I bet u ten dollars it's because he's been taken in by a lonely old lady who feeds him sardines every day... and doesn't feel so lonely any more xxx