Molting is an annual event in the life of chickens wherein they lose their feathers (a few at a time), to be replaced by new ones. From what I've read, they usually start with the longest wing (flight) feathers and then move basically from head to tail, so you should check the wings to see if the flight feathers are all there. I believe they have ten flight feathers on each wing, and they lose them in sequence starting from the tip of the wing on back. That's where I would look if I were looking for molting.
I will say that when I added new hens to my coop (twice), my ladies stopped laying. They'll either start laying again soon, or they'll take a break.
If you're looking for a good reference to have on hand, I've found Storey's Guide to Raising Chickens to be a valuable resource. It's got some pretty reliable information and has helped me not to panic needlessly about my hens.
