Hey,
its funny that you should post this, because we are having the same problem with our 7month oldboy.
He is pulling out his fur, just as your bun is, in the same area. (under the neck and chin) We had noticed a thining of his fur on his under side and bald patches earlier in the summer and took him to the vet. Our vet treated him for fur miteswith a course of 3 shots of ivermectin, and it seemed to have stopped for a while.
We had him nutered around 2 weeks ago, and have started to notice a big patch of skin exposure, but his fur isn't thinning like it had when we treated him for mites.
Does anyone else have any other ideas that might help both our buns out?