PEDRO REY/AFP/Getty Images

Last week, I noted that rogue French trader Jérôme Kerviel had become a minor-league Internet superhero, largely through Facebook fan groups. (Today, the member count for the group "Jérôme Kerviel should be awarded the Nobel Prize in Economics" stands at 2,813.) But along with online jokesters, Facebook's members apparently also consist of highly motivated social activists.

On Monday, hundreds of thousands of Colombians, along with supporters around the world in nearly 200 cities, led protests against the pro-communist rebel group, the Revolutionary Armed Forces of Colombia (FARC). The protests aren't unexpected—the rebel group has been terrorizing Colombia for more than four decades—but the method of organization is what's novel.

Roughly two months ago, after photos and video of FARC captives surfaced, enraged people began to join the Facebook group Un Millón De Voces Contra Las FARC ("A Million Voices Against FARC"). The group then grew with incredible speed to include more than 280,000 members, publishing its pleas for "No More! No More Kidnapping! No More Lies! No More Murder! No More FARC!" in Spanish, English, French, German, and Portuguese. The resulting protests are some of the largest ever seen on an international scale. Not bad for a Web site that started out as a networking platform for Ivy Leaguers.