Recently, a 15-year-old named Kylie tweeted her suicidal thoughts, and a Twitter account called @KillYourselfKylie tweeted back a series of ugly responses. These included "We have 3 b----es who should cut and drink bleach" and "I think i just made someone cut herself yayayyyy" and "We hate you just die . . . " That last note was followed by a list of six first names — apparently teen-agers who knew Kylie.

"Thats it. Im done," Kylie wrote back. @KillyYourselfKylie replied, "I WILL NEVER LET YOU IN PEACE . . . NEVER!!!"

At this point, the Internet groups Anonymous and Rustle League showed up in Kylie's Twitter stream. "We'll get to work on this problem NOW," one message promised. Another one addressed itself to Kylie's tormenters, "So, you think this is FUNNY? Let me introduce you to the REAL Internet Hate Machine, you dumb-a-- bullying Twats. Game: On."

What followed, in an exchange collected by the Daily Dot, was a series of threats and mewling apologies. The Anonymous and Rustle League rescuers threatened to post the full names of the teen-agers who'd been goading Kylie, unless she made it clear that they'd apologized. When Kylie reappeared on Twitter — blessedly tweeting thank yous to her supporters — she found messages like this one waiting for her: "It's nice to see the power of twitter do good. It's a new day for you, @YayyImKyliebaby. A new beginning, with your new friends."

I'm not in favor of outing minors for their online misconduct, but I can't read the full Daily Dot account without cheering for Anonymous and Rustle League. In writing about bullying, I've seen too many posts, on several social network sites, in which kids suggest that other kids should go kill themselves. I find it utterly dismaying and weird — why on earth would anyone court that kind of danger? Think how these kids would have felt if Kylie had taken their bait. I agree with Laura Beck at Jezebel that it would have been nice to see some of Kylie's peers step up to defend her, but in their absence, I'll take the adults who showed up this time to police the Internet. The personal attack on Kylie is much more harmful than spewing racism about President Obama, however gross that is. The Web can make life worse for vulnerable teen-agers — and, this time thanks to Anonymous and Rustle League, it can also make life better.

Another example of good online citizenship: MTV's efforts to get kids to out themselves or people they know for crossing over from "digital use to digital abuse." This is happening on a popular app called Over the Line? The app hosts more than 6,800 posts, like this one: "Okay soo this boy ask 4 a pic of me without a top on, cause he sent me a pic of his . . . I really don't want to. . . . Idk wat 2 do HELP!!!" Users can post anonymously or by name. Other users vote on whether the behavior described is over, on, or under the line — meaning, socially acceptable or not. (Being asked to send a topless photo when you don't want to: definitely over the line.)

Now MTV is rolling out a new feature, based on a partnership with a lab at MIT. The lab designed an algorithm that categorizes users' stories and then helps them find other stories that are similar in terms of subject matter. The idea is that kids posting about bad online behavior will know they have company, and with luck, will find comfort in seeing their own troubles in the context of others' struggles and solutions. It's crowd-sourcing, by and for teen-agers, about the boundaries of online behavior.

"We wanted to help our audience come up with their own answers," said Jason Rzepka, senior vice president of public affairs for MTV. "Rather than us putting up a list of digitals do's and don'ts, it's more valuable to ask them to collectively draw the line between what's innocent and appropriate, and what's not." The evidence that MTV's approach speaks to its demographic comes from the time users spend with the app. They've posted more than 350,000 story ratings and spend seven minutes on Over the Line?, on average per visit, which on the Internet is enviable.

It was a relief to think about the good the Web can do as I read "Oddly Normal," New York Times reporter John Schwartz's sensitive and perceptive account of his son Joe's suicide attempt at the age of 13. Joe was gay but just coming out when he swallowed handfuls of pills, and he spent a couple of weeks in a locked psych ward after his parents found him in the bathroom. In the period that followed, Schwartz watched his son in fear and then tried to analyze what had gone wrong, at home and at school. He's willing to write about "our own missed clues along the way, so agonizingly clear in hindsight." The best thing about this book is that it's not about blame: It's about understanding. Even the mean kids — so often lately the target of "bullycide" narratives — aren't portrayed as ogres.

Schwartz explains that gay teen-agers are at higher risk than straight kids for attempting suicide, and he talks about the way in which it was harder for Joe to find social acceptance. There was no Gay-Straight Alliance at his middle school, for example, and those groups can be a crucial buffer for kids who are unhappily questioning their sexuality. But Schwartz doesn't demonize the kids who made stupid comments to his son about sex and homosexuality. "It wasn't harassment, since they didn't know he was gay," Schwartz writes. "But because Joseph knew he was gay, the comments — and the fact that he didn't feel comfortable participating — increased his sense of isolation."

It's profound isolation that the Anonymous/Rustle League intervention for Kylie, and MTV's Over the Line? tool, are trying to combat. For some kids, like Joseph, there is help to be found at home — by the end of Schwartz's book, I felt like his son's great luck was to have two parents who made mistakes, sure, but who did their utmost to learn how to support him. That's still the ideal. But even the best parents can't protect their kids from everything the Internet serves up.

Bazelon (@emilybazelon) is a Slate senior editor and writes about law, family, and kids. Her forthcoming book "Sticks and Stones: The New World of Bullying," will be published next spring.