More details are necessary in order for us to help you. Did it happen during the day or at night? Were your chickens in a coop, run, or free ranging? What is your coop, run or tractor built of, if you have them? What is your setup like? I'm glad you're asking questions - this is a great place to learn. In the future, you might want to consider asking them all in one post. That way people will be able to read and answer them all in one place.
Racoons will reach through the wire cage, shake the cage, tip it over, or tear it up. Dogs are also able to get into many cages. You need to build a better coop!!! Mary
Agreed. They also can learn to open latches. Putting a chicken in a wire cage outside is just feeding the racoons. The birds need a safe indoor coop area at night.