Kitchen faucet - frozen...can not locate frozen pipe?

our kitchen faucet and in-door water dispenser on the fridge do not work. Every other faucet/toilet in the house works. I have looked under the sink and the pipes come up through the floor. I went into the garage (which is under the kitchen) and there is one large plastic pipe across the ceiling, not sure if that's it, the garage isn't even cold, not sure how it could be frozen. What is the best approach to thaw this pipe? Where could it be frozen?