Put posters up everywhere and hand out leaflets to dog walkers, posties, binmen, etc.
Contact dogslost (leave them a message + see who their local rep is on there as well)
http://www.doglost.co.ukAre you in an area that runs near another local authority - if he's lost his collar or tag then someone may have taken him to another local authority area (if people don't know an area they pick a dog up and take them to their destination area and leave with dog warden there - its my local dog warden's bugbear)
Keep ringing dog warden - vist their kennels regularly as well jus tin case he's been missed
Ring round every vet, local rescues.
If you give me details then I can post on k999