* 十代 (じゅうだい, jūdai): This literally means "ten years," and refers to the teens (10-19 years old) as a whole. This is the most common and accurate way to refer to the teenage years.
* You could also say the specific age, like 十六歳 (じゅうろくさい, jūrokusa) for sixteen years old, 十七歳 (じゅうななさい, jūnanasai) for seventeen, etc.
Therefore, the best way to say "teen" in Japanese depends on what you're trying to communicate. If you're referring to the teenage years in general, 十代 (jūdai) is the best choice. If you're referring to a specific teenager, you'd use their age.