Don't worry,  as you may already know: "normally" a trailer does not need liability insurance, so DMV will not suspend your driver license or registration because your plate got stolen, and therefore you will fail to surrender it.
So, just to make sure: do I need yo surrender trailer plates?
You must surrender your plate if your trailer doesn't have a valid registration, it's ok if you "lost" it as long as your registration is valid.
another asked how about registration. What should I do if I use the truck without the necessary modifications?