The white color to the mouth indicates something serious is going on and that could be anything from system shut down from a disease like parvo, to overload of worms, to a heart problem, to being in shock from eating something he shouldn't have.
You need him to see a vet as soon as you can if you want to save him.
On your way to the vet try to keep him warm and see if you can give him a little Karo syrup, pancake syrup, or sugar water to help him have some energy.
Hope this helps you and good luck!
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