My boy was waking up wet a lot older than is typical, and here is what we did. We happened to have some plastic graduated beakers that held about 800 ml and were clearly marked to measure volume. I showed him how to read the volume on them and we kept them in the bathroom. I encouraged him during the day, when he was home and could go to the bathroom whenever he wanted to, to try to hold it a little longer each time and see what he could get that volume up to. This is sometimes described as "bladder stretching" but I think it was really more about being aware of the sensation of needing to pee, but not immediately peeing in response to it. We are talking about a child old enough to understand 3 digit numbers, a child who goes to school and goes on sleepovers etc. Not a 3 year-old, more like 5+ or 6. Old enough to pee into a cup, note the number, pour the pee into the toilet and rinse the cup.
The theory was that over time, he would not just pee while asleep, but would resist the urge until it got a little stronger, strong enough to wake him up. And in the meantime he would feel that he was doing something towards waking up dry.
Did it work? Of course. Well, something worked. Perhaps time passed and his bladder got larger. Perhaps he learned to wake up or he learned to sleep through. Perhaps doing something about it got the message across that he could change this, without making him feel bad for what was happening. Whatever the cause, he began to wake up dry more often than not, and then the whole thing was just a memory.
Certainly a teen is old enough to buy into something like this. It's not behaviour mod or sleep alarms, and clearly he has either less bladder capacity than those who can sleep through, or less awareness of the need to pee than those who wake up. So perhaps such an exercise can help.