I have fifteen pet chickens who live outside in a large coop i built them. I take very excellent care of them and like them dearly. I have one show chicken who survived a dog attack and is now at my ’safe house’ to spend the rest of her life in peace, she is fine. I have one chicken who has a bent beak so i have to hand feed her, she is fine. I have a brother and sister (dont know the species) who also survived a dog attack and the female is fine. The above chickens share a cage. The brother (whom i should point out is really a girl, but i named him Edgar when he was a baby and it stuck.) He has a bald patch on his left wing and there are feather shafts in his skin, just no feathers. I thought he was moulting, but nothing will grow. He is now developing a bald patch on his breast too. IDK what to do. I like my chickens and would heartbroken is something happened. Is he sick? Can i fix it?? Please help. 
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There are really multiple things that could cause this.
Mites: Your birds could have mites, or lice. This would cause them to be uncomfortable and yank out their own feathers. To check you would want to ruffle through their feathers (don’t worry they are bird mites/lice you can’t get them), they typically gather near the bird’s vent. If you notice them get some mite/lice powder. Also, make sure your birds have dry dirt to dust bath in, this helps suffocate the creepers. If you have leg mites (upraised leg scales) rub them down with some oil, olive oil, butter, bag balm, or something else similar. This can also be used in heavily affected areas.
Spacing: In tight spaces, birds in their boredom result in feather pecking. They will eat the other bird’s feathers. Sometimes this is also a protein issue, but it seems like you take very excellent care of your birds, and you’d notice such a thing. If it is spacing, try to give them more room, and make sure they have something to root though, give them some dry leaves, or weeds, or something.
Molting: When a bird molts he looses the whole feather, not half of it. An no bird should typically have just a wing with spikes. Feathers would also be growing in.
Breeding: Some birds have terrible bloodline for feathers. I once had a silver-laced Wyandotte with terrible feathers; she was a bird with sticks, as she had no feathers, just shoots. And when you would pick her up, they were brittle and would break. She had this problem for years, until her death. Some birds also like frizzles, if they are crossed with another frizzle will produce chicks with terrible feathers that break very easily.
Hope your small guy feels better soon, and if you have any questions feel free to contact me via email,
Jamie/Rhode Runner
seems like he sick to me why be heartbroke yes they are chicken and your pets but if you buy them as a chick like i did they come cheap $5 a chick. i like taking care of chickens. Maybe he is pulling out his own feathers or is molting. Or getting attacked by other chicken. You can try and take him/her to a vet that specializes in birds and chickens or googl this problem. i hope it aint a male the males are always a hard loss ): especially in fights.