Still losing feathers.

I'm completely out of ideas on this.

Since I moved the girls I've noticed missing feathers from the neck area. I though it might be feather pecking and didn't pay too much attention. When it seemed to be spreading I thought it might be crawlies - either on the birds - lice or mite or in the coop. I cleaned the coop completely tested all the wood joins with paper and then applied a blow torch and poultry shield. I didn't see anything more than the odd fly even at night checking with a torch. I've also scattered diatoms over the girls, in the coop, nest box and in their dust bath just in case.

Tonight after playing chase round the garden  I managed to grab my leghorn and shes almost bald around her breast.... I still can't see anything on her, as far as I can tell there are no crawlies and no eggs. 

They have continued to lay daily without any problems, I think they may have missed 2 days each in 3 months or so.

What are my options ? Other than a trip to the vets. I know it depends on what the problem is but I completely out of ideas. Can I get a spay or something just incase theres something on the girls Im missing or can't see.

I had them September 2008 at point of lay so they're just over a year old.

Other than being a little flighty and looking rather moth eaten they don't seem to be in any distress.