Chicken losing feathers

I have a few chickens that have lost most of their feather. At first I thought it was a molt but I have one chicken that has been "naked" for a year. Now my rooster is losing his feather on the top of his legs and around his neck......What do I do? How do I stop it? I have separated them, I've put them back, I have 1 rooster and 1 naked bird and 4 that are starting to lose their back feather. They are all my 3-4 year old birds, I do plan on butchering all of those guys(in about a month) is this going to effect the meat any? How do I stop this feather loss from affecting my 4 two year old phoenixes and replacement flock 18 chickens and 5 turkeys that are 4 months old?

 

Thanks it was lice or mites or something like that. I sprinkled them with Seven Dust and they have grown their feathers back. It really only took 1 day to work. I dusted down each bird and their nest area and left them alone for two days. They had new feathers starting to grow back on the third day. It's been over two weeks now and all of the birds have grown back all their feathers. I went ahead and dusted all my birds and there pens and everything seems to have gone back to normal.