Nowhere else to go

Hot shit, sorry. The site didn't send my comment. I'll sum it up:

Definitely tell a professional about his situation. Even if you can't manage to bring him along, at least you'll get some idea of how severe his problem is.

I'd recommend telling your immediate family, too. Therapy or counseling is a very important part of getting better — in many cases, family therapy is one of the keys to eating healthily again. Parents and other family members are important in supporting people who are battling an eating disorder.

Cognitive behavioral therapy (CBT) is considered the treatment of choice for people with bulimia. With the support of decades’ worth of research, CBT is a time-limited and focused approach that helps a person understand how their thinking and negative self-talk and self-image can directly impact their eating and negative behaviors.

While many medications may be prescribed for symptoms related to bulimia, only Fluoxetine (brand name: Prozac) has approved by the Food and Drug Administration for the treatment of bulimia nervosa. This medication has been found to decrease the number of episodes of binging, as well the desire to vomit, in people with moderate to severe bulimia. Unless memory fails me, I think the recommended intake was something like 60 mg a day. [Quick disclaimer: I may have studied human physiology and nutrition before, but I'm not a health professional. Seriously go and contact one.]

In the mean time, encourage him to eat less junk food and more easily digestible food. Bananas and yogurt are relatively safe bets.

Also encourage him to brush his teeth and use mouthwash after vomiting. The hydrochloric acid from his stomach will damage his esophagus if you don't neutralize it.

Ah, heck. Sounds like it's getting serious.

I personally think that trying to convince him to see a therapist is the best choice. Offer to shell out the bills and everything, I guess it's the least you can do.

Telling a professional and your family are probably your best choices here. You need to do this as soon as possible.

In the mean time, encourage him to brush his teeth and gargle mouthwash after vomiting. It's not going to make a ground-breaking difference, but it'll at least slow the effects of his stomach's HCL acid wreaking havoc on his oesophagus. If possible give him foods that are likely to be non-irritating to their gut and easy to absorb (eg, bananas, yoghurt, bread).

I'm really sorry. I'm not a health professional. I've studied a bit of biology (with a focus on human physiology and nutrition) but I'm an engineering/commerce major as of currently, so this is just my two cents.

Aside from that, here's a bit of research I pulled up for you:

Cognitive-Behavioral Therapy: There is general consensus that CBT is the best established form of psychotherapy for bulimia nervosa either in an individual or group therapy format (Mitchell et al., 2007). Other forms of therapy are being developed and researched to assess effectiveness with bulimia (see Feast of Famine: The Etiology and Treatment of Eating Disorders course).

Prozac (fluoxetine) at high doses (60 mg/day) is considered the “gold standard” for treating bulimia nervosa (Fluoxetine Bulimia Nervosa Collaborative Study, 1992). Fluoxetine has been found to significantly reduce binge eating and purging behaviors and is the only medication approved by the Food and Drug Administration (FDA) for these purposes. It may be a useful intervention for patients who have not responded to psychotherapeutic intervention (Walsh et al., 2000).

Source: http://www.continuingedcourses.net/active/courses/course038.php

I'd be careful about administering prozac, though. If I were you, I'd just try anything to get the boy into a professional's care. It's going to take a fair bit of persuasion, but think about the long-run.