For teenagers that can grow facial hair easily, it is popular to grow a full beard, it does not need to be a very full beard in thickness but should grow naturally.
Besides the good old fashioned goatee, there is also the chin strap, soul patch, and designs shaved into the beard by professionals, but my personal favorite is plain old clean shaven.
You may see teenagers sporting a mustache and sideburns combination, as these areas are often easiest to grow. The chin-strap beard is another popular one.
