So, I checked the car when my girlfriend got home and sure enough, the faceplate was nowhere to be found. She called the number on the keytag today and spoke to a woman who said nothing of that description had been handed in (well duh, if it was stolen it's not gonna be handed in, is it?) and she'd call us if it was.
Unfortunately, there's not a lot we can do. We might drive over there tomorrow and talk with the guys, but frankly I'm not sure if it'll just be a waste of time and gas. We should probably just chalk this one up to experience and be WAY more cautious when dealing with valets in the future. :/