If you do not know where the pipes are frozen, take an all metal knife or spoon and tap lightly on the pipes until you hear a significant sound difference (more solid). Now take a hair dryer and begin passing the dryer over that small general area. Try not to concentrate the heat in one specific spot. This will melt the ice jam. This does not guarantee you no leaks. The pipes may already be split and the ice melt will cause them to leak. Make sure someone is standing by the main shut-off valve in case it does leak. And
remember, he who hesitates.......GOOD LUCK!!!

In my haste I forgot to mention to open your hot water faucet to allow for expansion and so that you can hear when the water begins to flow. You can help to prevent this again by letting the water trickle out of the faucet while not in use.