Reserve Buffalo Style Sauce packet from Chicken Bites for later use. Bake Chicken as directed on package; cool slightly. Cut into bite-size pieces.
Spread pizza sauce onto pizza crusts to within 1 inch of edges; top with chicken, celery and cheeses.
Bake 10 to 12 min. or until edges of crusts are golden brown and cheeses are melted. Meanwhile, thaw Buffalo Style Sauce as directed on package.
Drizzle pizzas with Buffalo Style Sauce before serving.