Our entire flock has stopped too. A mixed flock of Barred Rocks, a Dominique, Andalusians, Ameraucanas, bantams and Hamburgs. Some are around 18 months, but the younger ones are only about seven months old. A couple of the older ones are molting, so I can explain a reduction, but the younger ones just abruptly stopped, almost like, oh, the old gals aren't laying, so I'm not either. This didn't happen at all last year -- we were overrun with eggs all year long. We will occasionally get an egg from the Dominique (7 months old) and one of the Barred Rocks (18 months) but that's about once a week.
No traumatic events, no scares, feed is good, nesting boxes are good, no hidden nests, no egg eating. I heard from someone over in Chapel Hill area (about 20 minutes away) that there is a group of chicken owners that way having the same problem. Bizarre. I will have to buy eggs this week for the first time in over a year.
Any other hypotheses out there?