Unless he is 18 at the time of travelling, your son will have huge problems finding accommodation. To stay in hotels and hostels in Europe it is necessary to either be 18 or staying with a responsible adult eg parent or older sibling. While you might be able to book hotels on his behalf, actually checking in to an hotel is a contract between the hotel and the guest - and minors cannot enter into contracts!
As for where he should go, that is dependent on his interests, what he wants to see, and what his expectations are. There are nearly 50 countries in Europe, and each one is different. Surely he has some ideas of what he wants to do. And where he goes, how many countries or cities he visits, also depends on how long he will be travelling and his budget.
At that age my first trip in Europe solo was Rome. If he's into pizza, history and architecture it will be a dream come true!
Italy, Rome. Canary Island.
Alba Iulia - EDEN 2012
He will be far safer in Europe than in the US.
Really doubt his parent is writing this.
Spain. He will be an adult anyway
Scotland ;)
