As SK above says, put posters up in your surrounding area, shops, on lamp posts, bus stops etc saying 'unneutered male cat found and [approximate age] contact [000] if it's your cat!'.

If anybody calls, get them to describe him to you, colour of fur, eyes (probably still blue if he's kitten young) and any characteristics like a scar, bit of ear missing etc - Obviously if it matches his description then you've found the owner.

Unfortunately full young male cats will wander and, if he's escaped by accident, he will just keep on wandering!!

Good luck.