@Welshies ... Do you have dogs? Is your chicken coop near your home?
You say you have twenty acres. That's a lot of land. If someone were to take your entire flock in the middle of the night, it seems unlikely you'd see blood and feathers. Chickens are zombies when they're on the roost. I would imagine anyone could quite easily pick them up, one at a time, and tuck them inside a rucksack or pillow case without much of a fight from any of them.
And if they had the time to grab most of your large flock, then why leave a few behind?
Also, wouldn't it be hard for a car or truck to go unnoticed on your property? So, did they arrive by boat on the river and walk in just to grab your chickens? Someone a few months back posted a discussion about something very similar. They ended up seeing someone come back the next night and taking more chickens.
But in a very short amount of time, wildlife can remove your entire flock and hide them, with little to no evidence that they were there. That's what I feel happened, and a fox does seem like a likely candidate.
I've been thinking about this all day and feel just terrible for you and your wife. If my dogs hadn't needed a midnight outing a month or two ago, I wouldn't have discovered the chicken door I left open to their coop, and since we live in the woods and have lots of predators, they could have all been killed. It was truly an awful feeling.
There are some great discussions on hot wire. Lots of folks strongly urge others to wire their chicken runs. They offer all kinds of good information on what and what not to do. I may follow suit one of these days.
Thank you for starting this discussion. I've learned an awful lot. I'm just sorry it was at the expense of your precious chickens.