The police can confiscate plates if they are fraudulent, are not for that vehicle, or are evidence in a case (such as a false registration sticker situation).
No, you can't drive without 2 plates on the car. Both a front and rear plate are required under Vehicle Code section 5200.
I am in 100% agreement with Mr. Kaman - please ignore comments from attorneys not licensed to practice in the jurisdiction where the question is posed. They're usually guessing. Worse, they're often wrong (as is the first answer...).