Well really you can eat anything if you want too if you're a vegan but then it wouldn't make you a vegan anymore.
Anyway yes you can eat some kinds of Pizza when you're a Vegan.
Dough of the pizza is vegan but thin crust pizza is not vegan since it contains dairy.
The sauce as well is vegan so as long as you don't order a Pizza with thin crust, cheese or any meats then you can eat the Pizza as a Vegan.
You can request a vegan pizza be made when ordering pizza and most if not all pizza shops should know what a vegan pizza is and how to make the vegan pizza.