I think you should post on Parent Emeritus because that's the forum for adult children. You have a different relationship and different choices when your children are over eighteen. For one thing, you don't have to fund them. For another thing, you can draw a line in the sand and say, "You get a job by Aug. 20 or we pack your bags." Stealing is usually a sign of drug use...they steal to buy...but they are not ambitious and don't want to work. I would search his room, check his Facebook and cell phone. The poor guinea pig will probably starve. This is a troubled young man and there is no simple fix nor can YOU fix him anymore because of his age. It is on him now and you and your wife have to sit down and decide what to do about it.
Is he going to school? Helping around the house? Doing ANYTHING? Any early diagnoses or troublesome history? Are you his father? Does he refuse help? Something more is going on here and you don't discipline a nineteen year old like you do a sixteen year old or a ten year old. If he won't work, he doesn't need a cell phone or internet or car insurance because he is old enough to pay for it, plus pay for any gas or car insurance. Why in the world did he get a free nice truck???? All of my grown kids had NO car of their own until they worked and bought one and had to help pay insurance and gas when they drove OUR transportation. They grew up with good work ethics. My younger two will have to do the same or they won't be living here. However, I don't anticipate any problems with this. Your boy is being treated like a child. Are you maybe a stepfather who doesn't know what to do about mom babying him and allowing him to get away with stealing?
Again, I higly recommend Parent Emeritus and welcome to the board, although sorry you have to be here.