It's time for CSI: Poultry Division!
Did they all look sort of like that? With the feathers chewed off the necks? Is it just the feathers & skin or also the meat off the necks? Where are you finding them? Near a fence with the body on one side & the neck & head on the other?
Raccoons are opportunists and if they can find more & better food during the daytime they'll change their sleeping habits. Just because a raccoon is out during the day doesn't mean it's rabid. Often they'll grab a bird through the fence wire and pull it through to eat it, often starting with the head.
Dogs will often just play with a chicken it catches, gnawing on it like a chew toy but not eating off much meat, just skin & feathers. I've had birds killed by dogs who just had their necks broken but little other damage. Other times, especially with the roosters, they gnaw on the tail feathers.
Are your birds kept in a coop/pen, or out free-ranging? Are there trees/woods near their coop? Is your lot fenced? How easy is it for a dog to get in?
Certainly strengthen your coop security & the fences around them. Maybe you could put electric wire around your coop and keep it on during the day. If possible, rake the ground smooth around your coops, perhaps even broadcast some flour around it. Then you can better see & identify the tracks of any animal coming around.
Put your deer-hunting tree stand up near the coop and wait to see your predator.