Lift up the existing feathers and see what is going on. Are there holes where the feathers used to be? If so you might have a pecking problem or mites or lice.
If there are pin feathers coming in then they are probably moulting. Give them extra protein and some poultry vitamins in their water and they will be just fine.
When my hens start to molt, their neck feathers get thin and then they lose their tail feathers. A drastic change in feed can also trigger feather loss. As purpletree23 said, extra protein will help speed up feather growth.
Just wanted to say thank you for posting this info. We live in coastal Northern California and my 9-mo Jersey Giant, "Snuggle" has a ring around her neck of what appears to be just the feather pins. I searched and got this info immediately. You guys are sooooo great!! Thanks!!