I was that teenager, OP. (really need to change my username!)
I went through a situation 33 days before my first trip abroad, which had taken years of saving. This situation triggered my anxiety to the point I was diagnosed with Generalised Anxiety Disorder. I was 14, then.
Have you talked to your son? I ask because my parents' first instinct was to cancel the trip, and I will be eternally grateful they didn't. What is it that he fears? What can be done to ease a trip?
This is me: My phobia is about vomit. These things help me: Taking an anti-emetic before a flight, sleeping through it so I don't hear/smell someone being sick, self catering so I don't have to try strange foods.
I would also consider medication. I've been on ADs since I was 8 and it makes an enormous difference. It can take a while to find one that works; I've been through half a dozen until one worked, not to mention a few months before you can know if it will work on not.
Also, could a benzodiazepane be a solution short term? They need to be very carefully monitored because of possible addiction, but it works within minutes, so they are fantastic for panic attacks.
Don't give up on your son, ok? It will get better.