Well, we've done two cruises in Europe in the past 25 months...
The first one, to the Baltic on Princess, we took our daughters, then 15 and 17...The average age on the ship had to be 85...and there were only about 12-20 teenagers on board...(Luckily, most everyone on the ship was English speaking)...Despite the dearth of kids, our daughters nonetheless managed to form into a tight knit goup with most of the few teens that were there and managed to have a good time...
On our just completed Mediterranean cruise on Celebrity, there was a far younger demographic...including several hundred kids, spanning all ages...There were about 500 French folks, 500 Spanish and some Italians, but most everyone else was English-speaking (Americans, Canadians, British, Australians et al)...It seemed any teens travelling would have no trouble finding other teens...
I would also think Royal Caribbean would be a good shot for a family demographic in the Mediterranean, perhaps even more so than Celebrity...That's where I'd look first if that's your greatest concerm...but look into Celebrity as well...
Good luck...
