Hello Mattalyn!
What you need to do, is pick up a chicken that looks questionable, and look near the vent area, way underneath the feathers, near the skin. If you see some creepy crawlies, you've got a parasite problem. Some people will check at night, because certain parasites are very elusive and hide well during the day, so you may want to look at a hen in the evening with a flashlight.
If you do see mites or lice, then you can dust them with Seven Dust (or poultry dust) from the farm store. You just powder them up from top to bottom, and repeat that around 10-14 days later to kill the eggs that hatch.
If you've got parasites, also, you'll need to clean out their coop real good, and powder it up too.
If you don't find any parasited, you may be right about the molting and the rooster. Sometimes, if chickens are cooped up alot during the winter, they will get bored and start feather picking. Look at your flock, and see if there is a chicken that looks perfectly fine, with no feather loss, and that would be your culprit! (I'd get rid of the feather picker if that was the case.)
Feather picking is also a sign of a chicken not having enough protein in their diet, but that shouldn't be the case if you're feeding a good layer feed.
Good luck!
