Just read this thread and i feel for you mate, I really do. I used to be a dog warden so know they do turn up. As others have mentioned try the dog warden and keep on at them, also try local vets, police and kennels, also keep your eyes peeled evening and morning when the new "owner" could be walking her. Leaflets and posters also work, I lost a dog a few years ago wiho had lost her collar but she was picked up at the roadside and the person saw a poster and returned her. Good luck.