Shows how little you know about both introverts and eating disorders, no offense or anything.
Party bulimics, those that do it because their friends do, sure chances are they'll be extroverts.
Introverts can be plenty concerned about their image. It's how they convey themselves without talking. Also, look good and chances are the boy will come up to talk to you vs you having to instigate it.
Typically, however, eating disorders have little to do with trying to make yourself look good but more with loss of control and regaining control. For example, if you are someone with undiagnosed mental health issues- let's say bipolar because your moods are often fluctuating for what seems to be no apparent reason- and you feel like there's so little about you that you have power over, well, not eating is a good way to exert control over yourself. Not to mention, not eating can give you a sort of feel-good buzz, like you get after lots of exercise.
I think this is another reason introverts may be more susceptible to eating disorders. Often introverts have a hard time expressing their pain or needs or desires out loud so their problems can often not be solved. Or they tend to try and solve their problems on their own by self-medicating with drugs, food (or with-holding food), cutting, etc.
I don't know what types are most likely to get eating disorders- if there is any sort of correlation whatsoever-but I do know that most of the INFPs I have known have had issues with it at some point in their life, myself included, pretty much as a result of depression.