Personally, I pegged Dylan O'brien as an ENTP, simply because he seems to fit the ENTP 'visionary' profile and (when asked introspective questions) actually gives very thoughtful answers. But I could see him as an ENFP as well.
Actually, Dylan said that despite his career and portrayal of Stiles, he's introverted and socially awkward. I think introverts are more common in performers and, in particular, comedic actors, than expected. It's a way of having a ready made mask. You're not really being 'you' in performances. And, screen performances involve relatively small groups and a SCRIPT which I, an INTP, would really appreciate.