[As a side note, I really don't know why I've started watching this show, I guess cause it's on instant play and I'm taking an easy break from the x-files. Clearly the show isn't worth, well, anything, but I can't help but think about MBTI when I watch...I'm on season 4 now]
I don't really understand why people think Spencer is an Extrovert. The guy has no friends (and not just cause he's a douchebag, I'm sure there are plenty of bros who would jump at the chance to hang around him), he sits at home all day and reads/goes on the internet, he doesn't have a single clue how to socially interact, he's insanely jealous, likes to be alone at home with Heidi, he seems to have a problem with every single person, with the exception of Heidi. I personally, think he's an ISFP. I think the SF is pretty obvious, but most people pegged him for a J - but when Heidi or Stephanie are not around to clean, the place goes to shit. Not to mention, the lack of a job or any apparent ambition to do anything in life. ISFP's highly prize loyalty and are very sensitive, two things that Spencer is very obsessed with. Whatever personality type he has, he's clearly the "gone wrong" version.
Heidi - I thought ESFP in the first season, but once she got into her job at sbe and started to get serious about her life, she really changed. I feel like in the later seasons she seems more like an T - possibly an ESTJ.
Lauren - ENFJ
Lo - INFJ
Whitney - ENTJ
Audrina - ISFJ
Stephanie - ESFJ
Justin - ISTP
Brody - ESTP