It depends upon which ship you are sailing on.
The newest two NCL ships have rock climbing walls and bowling alleys.
The Spirit has a topside disco and large game room perfect for teens. Facilities aboard the ship aren't the only consideration. Activities are also important, such as dance parties and other teens aboard the ship. Plus the Excursions you book while in port.
Each itinerary and ship have different possibilities to entertain your teens.
If you were to post which cruise you are planning to take, and which ship, I'm sure others will reply with more specifics.