I think my son ate his pizza on a Fleishig plate. That plate was washed in the fleishig dishwasher with a lot of other fleishig dishes. What is the status of the dishes there? And the dishwasher?
In retrospect, the dishwasher and the dishes are still kosher. Regarding the dishwasher, the amount of cheese or absorbed taste that would be on the plate is nullified by the sixty times of the water and other plates. The other plates are also kosher, because the questionable plate is botil in the other plates. Additionally, assuming that the pizza as bought in a store, the pizza itself was only a kli shlishi, (from the oven to the pizza box, and then to the plate), and even if it was heated in a toaster oven at home it would be kli sheini, which is questionable if it will give absorbed taste to the plate at all. To add to this, it is quite possible that the pizza wasn’t yad soledes bo. Besides, you are not even sure if the pizza was put in the fleishig plate in the first place.
Adding all of this together, you do not have be concerned about it.