Hello there and Welcome to BYC!
I picture would help. I could be molting or even mites. However many times missing feathers from the neck area can be from aggression from other flock mates. They love to go after the neck, tails or butts when being aggressive. Sometimes they pluck feathers for more protein as well.
First, make sure they are on a good diet. Much of the time they pick on each other because they are bored and cramped in. So make sure they have enough space....5 square foot per bird in the coop, 10 square feet per bird in the run. Give them things to do...hanging cabbages or veggies, seed blocks, mirrors, ladders, things to climb on....anything to amuse them to keep them from picking on each other.
As for any bare skin showing, spray on some blu-kote to the neck area so the others will not keep picking at this bird. If you know who is the bully, you can separate the bully out for a couple weeks, or even use pinless peepers on the bully.
Also, do a good look on this bird to make sure this is not mites or lice. They can lose feathers where there are mites present.
Good luck with your flock and welcome to our flock!