Legal Question in Technology Law in California

I believe this is covered by Penal Code section 319, which defines "lottery" to include raffles except those conducted in a certain way by an authorized entity, generally a charity. The law refers to payment of "consideration" as an element of a lottery. Although no cash would be changing hands in your scenario, I'm reasonable certain that use of a commercial Web site would be deemed consideration from the user to the site operator, so I'd say the scheme you describe would likely meet the test for an illegal lottery.