How convinced are we that Anon sided with the right person this time?
I didn't even read the article or the twitters, nor do I care - I don't want to discuss this specific case. Assuming the person was being bullied and she's now marginally safer, it seems Anon did good.
However:
1) It's easy to make something appear different than it really is - just look at all of those videos of teachers or cops or others doing things that are "totally unacceptable and totally uncalled for"; most of which turn out to have been the reaction to prolonged taunting, excessive name-calling, etc etc. Anon isn't exactly known for thinking before acting.
2) Bullying bullies anonymously isn't the right way to solve this sort of issues. If it was, a teacher's job would be a lot easier. Anon might've gotten these perhaps-just-slightly-misguided teens in just as much psychological hardship as the original victim.
3) Convincing someone not to drink bleach/cut her wrists/whichever way she'd choose is obviously a good thing, right? Unless it's a new way for her to get attention and she's not, in fact, suicidal but more bipolar and looking for attention. Mind you that that isn't necessarily "better" and I'm far from saying that would mean she's doing it "for fun" or whatever; such cases need to be handled carefully and on a case-to-case basis. Getting 100 followers on Twitter to tell you how good, awesome, cool you are, how unique a person; how you shouldn't let life get you down and how everyone who's mean to you just doesn't understand you, may be a good short-term solution but it may get her even further from where she needs to be in the long run. That is, (ab)using Twitter for positive feedback because of things you might do is just another step in the cutting-yourself/attempting suicide/abusing drugs/entering selfdestructive relationships list of ways to try and get attention in all the wrong ways.
Does she need help? Definitely.
Do those bullies need to stop and taught that what they're doing is wrong? Yes, preferably. Or shot into outer space, I'm not that picky when it comes to the real bullies.
Are Anon the people to do it and Twitter the medium to do it through? Hell no.
Besides, "Anon" didn't do anything good or bad. A couple of dozen - maybe a couple of hundred - people did something good.
I still maintain that Anon is this era's "angry mob". Perfectly respectable people can do absolutely horrifying and shocking things in a mob, once you take away their identity. In that aspect, a mob (or Anon) is no better than a drafted army, except that it's voluntary. It's an escape into non-responsibility.
The problem with anonymity is that it "breaks" most moral rules. Whether it's the Bible (do unto others as you would have them do unto you) or Kant (Act in such a way that your way of acting can and should be taken for a rule for all men), or game theory (tit-for-tat and start out good - only betray or hurt those who have hurt or punished before), they all involve a certain amount of reciprocity.
Will some people still behave good when they know they'll never face consequences? Sure. Good people will. Most people would gladly steal/lie/cheat/heckle/hurt if they were guaranteed to get away with it, though - and that's exactly what Anon offers.
And yes, I'm perfectly aware that my style is easily recognized, I'm just posting this Anonymously for the Lulz. Of course.