I need some help, I snapped off a siezed plug!

Look in the socket for the piece that broke off. You should find the hex part of the steel shell with the porcelain still in it, you should also see the paper thin steel where it sheared. Normally the only part that stays in the engine is a thin sleeve of steel, threaded on the outside. If you heat it and use the correct type of easy out it comes right out.