Welcome to BYC, and I'm sorry about your lost chicken. How long have you had her? I have had a few not turn up at dusk in the past, but they usually were just outside of the run in the morning looking for food, and trying to get with the other chickens. I found 1 or 2 roosting in some shrubbery or low trees when I have looked before dark after realizing they were missing. If you normally take something out to your chickens as a treat, I would do that and call loudly in case she can hear you. Mine come running from everywhere if they see my red coffee can with scratch or treats in it. If she was a new flock member, she could have wandered off. Unfortunately I have also lost a couple to predators such as raccoons, feral cats, or hawks, and foxes can be very common as well. Sometimes I found feathers or part of a body, and sometimes not. I hope that you find her, and let us know.