Hi there, you need to get his energy levels up and maybe warm him up. How cold is your coop?
I would immediately do the following.
Move him somewhere warm and put him under a heat lamp.
Steep 10 cloves of garlic in boiling water, cool to room temperature.
Mix up honey and molasses and feed to him immediately.
Offer warmed milk and bread.
When garlic solution cooled to room temp add to garlic and molasses and offer in a bowl. If he won't drink it then you need to syringe or use an eye dropper and get it into his mouth - not down his throat - into his mouth and watch for him to swallow. You need to get at least three good squirts into him. If he drinks it then offer as free choice.
Put him under a heat lamp in a box filled with hay or wood shavings, or some sort of insulating material that is going to keep the warmth in.
Watch him.