First don't start it or drive it. A special tool is available through many parts stores such as Napa to remove the rest of the plug. Also be sure the threads are not stripped or spun. The tool might be able to be rented so you might also check that. Otherwise it will need to be towed to a shop that has the ability to do that type of work.
THERE IS ALL KINDS OF WARNINGS ABOUT THIS PROBLEM IN ALL DATA. FOR FUTHER REFERANCE YOU SHOULD LOOSEN SPARK PLUGS AND SOAK PLUG HOLES WITH CARB CLEAN FOR APPROX 1 HR TO BREAK DOWN CARBON DEPOSIT ON SPARK PLUG BEFORE REMOVING THEM. AFTER YOUU REMOVE ALL PLUG DRY HOLES WITH COMPRESSEDE AIR AND LET DRY, THEN INSTALL NEW PLUGS
If you have the 4.6 or 5.4 liter motor you may want to have the dealer do this,these two motors have defective spark plug holes,that have costed people thousands of dollars,Ford isnt do anything because it it will cost them to much.You can just google-"blown spark plugs on ford 4.6 liter triton motors" and read about it. BE VERY CAREFUL IF YOU HAVE A TRITON MOTOR