Feather-picking is one of the most exasperating problems to try to conquer. It's a form of cannibalism, and the chickens eat feathers because they crave the rich blood and protein that make up the feathers. It's important to try to halt the behavior before it becomes a habit. Everyone knows how hard it is to try to break chickens of a bad habit.
Feeding a higher protein feed like flock raiser helps prevent this, as well as adding BOSS to their daily ration. But to stop the feather picking, you really have to hit them with a lot of high quality protein, such as salmon and tuna.
Miss Lydia's suggestion to mask the pink, bare spots with Blu-kote is an excellent one. The chickens are drawn to those pink areas, and left exposed, they'll just keep plucking out any new, rich-in-blood pin feathers, and you will have bald chickens until the next molt.
I have one persistent feather-picker, and she's finally responding to daily feedings of canned tuna. I just let her eat as much at one feeding per day as she wants to eat. She seems to know her own protein needs and I quit trying to measure it out and guess if it was enough or not.
Also, the victims of her predations are growing new feathers, due in equal parts to painting the bare spots with purple Blu-kote and her finally getting the protein she needs.
By the way, Pick-no-more is also purple, but it doesn't stay on for even most of one day. It also smells very offensive, and putting it on the neck or head areas of a feather-picking victim is punishing to the victim, and has dubious value in protecting them. Blu-kote is odorless, but stains the skin and lasts much longer and the poor victim is unaware of it.