Put a “lo-jack” type device in the trailer.
Send private security to fetch it - AND the tractor trailer used to steal it.
Problem solved.
I think the issue is more complicated than that. Dispatch is releasing cargo to drivers for delivery on destination assignment sort of orders. In other words, a trucker comes in to dispatch with some creds and needs a load for a return trip, dispatcher assigns contract.... and away goes the cargo. It might not be until the stuff doesn't get to where it was suppose to go that they realize it's been stolen. And all the info given about the trucker is bogus.
I'm guessing as I only know enough about the industry to be dangerous. But I would agree, once you realize it's missing, the trucks/trailers should be pretty easy to find. They might be empty by the time you find them, but...