If they are free-rangers, you will always have doubtful success in finding all of their clandestine nests. Everyone that responded here has given sound advice. I would keep them up for a week in an enclosed run first, just to see if that does it. If not, then segregate to find out if you have an egg eater. As Minniechickmama said, Calf-manna is a good product that has helped some chook owners restore their egg laying. Egg-eaters cannot be reformed as far as I know. They would be automatic candidates for my freezer as much as I would hate that prospect.