The thugs must have the truck stashed somewhere (in a garage, in a warehouse, in the wilderness) as someone would have spotted the truck by now if they were on the road with it. My hope is the thugs have the owner with the truck and are trying to figure out how best to get out of the situation.
If they had killed him right away, I would have thought they would have tried to use his ATM and/or credit cards before people realized he was missing.
Another possibility is that all three ran off the road somewhere and were killed or injured. I can think of a dozen cases off the top of my head where missing people were later found in their vehicles off the road. Even when searchers knew the route the missing person was taking, they sometimes weren't found for weeks.
The situation's not looking good, but I don't think it's hopeless.