* נער/נערה (naar/nara): This translates to "youth" or "young man/woman." It's suitable for someone in their teens, but doesn't specify the age range as precisely as "teenager." `naar` is masculine, and `nara` is feminine.
* מתבגר/מתבגרת (mitbagar/mitbageret): This means "adolescent" and is a more formal and accurate translation, emphasizing the developmental stage. `mitbagar` is masculine, and `mitbageret` is feminine.
Therefore, depending on the situation, you might use either. For casual conversation, נער/נערה is more common. For more formal settings or discussions about adolescence, מתבגר/מתבגרת would be better.