Which type of veneers are used by celebrities?

Any and all! Celebrities need to look good for the camera! their smile is very important to their profession. It isn't what "type" of veneer, it is the skill that goes in to their making and placement that matters most!
Porcelain. The vast majority of veneers are made of ceramic. The most beautiful are hand crafted porcelain veneers. A skilled dentist and dental ceramist work as a team to create the best look and fit for each patient.
Ask their dentist . Better yet, ask yours. Especially if you are considering if for yourself or a loved one.
Reputation. It's not the materials used. All porcelain veneers are basically the same. It's the quality & experience of the dentist & the laboratory technician that determines the final esthetic result. I'm sure the celebrities seek out the most highly recommended cosmetic dentist & don't ask what materials they use.When you buy a car do you ask who manufactures the parts or go by the brand name & reputation?