Die-hard Andrew McMahon fan. I'm fairly certain he's an extrovert that uses the introverted feeling function (Fi) as his secondary. As an INFP I resonate strongly with his expressions. He's very in tune with the self and his own values/the nuances of his feeling, and most of his songs have that kind of flavor, which is much more of an Fi than Fe trait.
My guess would be ENFP. He's very introspective, but also very at ease in crowds and very physically expressive. In my experience, ENFPs often have some characteristics that look like introverts. The conceptual content of his songs makes me lean towards intuitive like the rest of you all, rather than ESFP

Also, he seems to use Si... his concerts often have certain patterns/traditions in them, and he throws in content that has a strong sentimentality to it designed to appeal to his longtime followers.