Before you run out and buy a pizza stone try using a well-seasoned cast iron pan with a sprinkle of cornmeal.
I also reheat leftover pizza on the stove top in a cast iron frying pan. I smear a thin film of butter on the bottom of each slice to create a toasted crunchy texture to the crust.
These days I keep a box of Elio's frozen pizza in the freezer and bake a slice in the toaster oven or buy a slice at the grocery store deli. Times change.
I have been wanting to do a cast iron pizza for quite a while. It is a lot like a pizza stone, in that you preheat the cast iron skillet.
But, since this is a frozen pizza thread, I have not tried cooking one on a stone or in a cast iron pan. It has always seemed to work out okay just on the oven rack. If you add a lot of ingredients to "doctor one up," I guess that could make a difference. Especially with veggies that may have a lot of water content.
I agree that reheating pizza in a cast iron skillet does work well. I would think you could do it in the oven just as well as on the cooktop.
CD