Can you post a photo(s)? Rooster removed feathers usually are on the back of the head, and back & back of wings. Molting feather can be anywhere. Pecking from other hens is often around the tail & vent. Self- pecking from parasites can be anywhere, but often around the vent. You need to pick up your birds and examine carefully for lice & mites- treat if you see any. If the birds are molting, you may see bloodfeathers. If the feathers were pulled out by something/someone- you should see regrowth in a few weeks, if the birds are otherwise healthy. If the feathers are broken off at the skin from rooster damage or other hens picking on them, they will not grow back until the shaft molts out on it's own- which may be several months or longer depending on when they 'decide' to molt. Photos again, would be helpful.