As has been mentioned, "official" means officially approved by the Akademio, and I don't know whether any particular word is or isn't. But as for words in common usage, the ones I've most commonly seen are "junul(in)o" and "adoleskanto". Both are somewhat more broad than the English word "teenager", which covers the specific ages between 13 and 18 or 19.

"Adoleskanto" is, I think, closer to the meaning of "teenager"; it literally translates to "adolescent", so indicates someone in that transition time between child and adult. PIV defines "adoleskanto" as "Junulo inter 14 k 20 jaroj" and "adoleskantino" as "Junulino inter 12 k 18 jaroj", but as far as I know most people don't hold to that narrow of a definition. ReVo's definition is broader, in regards to both age and gender; it reads simply "Juna homo seksmatura, ankoraŭ ne plenkreskinta" ("Young person who is sexually mature, not yet full-grown").

"Junul(in)o" is a significantly broader term; it literally means "young person" or "youth", and includes basically anything from 12 years old to 35 (different people have a different range of what they consider juna, so usage varies somewhat).

I myself, for example, am 23 years old; I wouldn't refer to myself as an adoleskanto, but would certainly still call myself a junulino.