Do you think i can use activated charcoal to whiten porcelain veneers?

Nope: The color of the porcelain is baked into the veneer. You will need to change the veneers to achieve your goal.

You cannot: Porcelain veneers are not able to be whitened like natural teeth. The veneers remain the same color, they are made of porcelain that never changes color. If stained they, can be cleaned with the rest of your teeth by a professional, dentist or hygienist.

No: You cannot whiten the veneer. It is a ceramic / glass / silicate/ zirconia, etc. non-porous surface. What you have is what you have. Can have them replaced with different shade. Some people may have luck whitening the tooth structure behind the veneer, but not common and likely not productive -- usually too much tooth to go through and often the veneers are opaqued and no whitening will show thru.

I'm afraid not: First, activated charcoal is not a tooth whitening agent. Second, porcelain crowns and veneers, as well as most composite filings, are color stable. Tooth enamel can be whitened, but to a completed restoration. Talk to your Dentist about your esthetic concerns and a discussion of available remedies.