Sometimes this happens to the best of us. There are many good posts on here about securing your coop and run and about predators. As you learn, you're able to fortify your birds to keep them from harm and safe from predators. Below are some links to those forums.Thank you. We started with 15. Now we are down to 10. Maybe we were not meant to raise chickens.

https://www.backyardchickens.com/forums/coop-run-design-construction-maintenance.9/
https://www.backyardchickens.com/forums/predators-and-pests.13/