It is sad to hear what has happened but I think I wouldn't give them the pleasure of knowing how upsetting it was (as hard as this will be) but do agree that it was more than likely a teenage prank, harmless to them but not to the victim.
On a positive note I have 2 sons and although not perfect (they can be a bit lazy unless asked) they have been so positive to have around during my treatment. They shaved when I did and my youngest son who is 18 also got the support of 10 of his old school friends who shaved as well. It was very emotionally overwhelming - so while there will always be teen ratbags around there are many more young people with good hearts.
Hoping you feel better