So to clarify... you only had one plate and it was missing? Or two plates and only one is gone?
If you still have one, drive the car. If you have none, don't drive.
Sucks but **** happens. Get a replacement as soon as possible. You did right to report it so when a major crime happens and your plates are involved you won't be in court for it.
Time to start collecting old plates. I have my old Colorado and Nevada ones hanging in the garage. I actually sent one from each set to a girl friend in Germany for her bar.