MOST PEOPLE who use Facebook or other social-networking sites post in-the-moment sentiments as their status updates: "Eating tuna sandwich" or "Got caught in traffic on the way to work."

But a glowering, beefy "OurSpace" user calling himself "Malcolm Jamal Smith" was up to more devilish doings this week: "organizing some broad street riots," he posted Tuesday.

While social-networking sites have helped long-lost classmates, colleagues and relatives reconnect, some mischief-minded users are using it for more poisonous purposes.

Police say rampaging teens who rioted in South Philadelphia Saturday night used cell-phone text-messaging and sites like Twitter, Facebook, MySpace and the new OurSpace, which caters to African-Americans, to assemble the mob.

Police estimated that 8,000 to 10,000 youths swarmed the area around South and Broad streets, hijacking a taxi, assaulting a woman yanked from a car, ransacking a convenience store and otherwise misbehaving.

Yesterday morning, more than 100 residents and merchants crowded the Palumbo Recreation Center in South Philadelphia to vent concerns to police bigwigs.

"This was a function of technology. Police ought to be monitoring those sites to see what's going on," one resident charged.

Deputy Commissioner Kevin Bethel assured residents that investigators are monitoring online activity to try to nab troublemakers and thwart the next cyber-stoked riot.

"The acts that occurred over the weekend were unacceptable," he said. "This is not a mandate against the youth of Philadelphia. However, we will not tolerate when these kids turn into bands and groups and prey upon people, brutalize people, injure people and then walk away from it," he added.

Mass mobilization by computer is nothing new.

Six years ago, the first flash mobs broke out in New York City.

Part party, part performance art, flash mobs were large groups of people who, tipped to an imminent gathering by social media, spontaneously converged in some spot to do something wacky: Have a pillow fight; applaud heartily for no apparent reason; break out in a disco dance.

Some have also used flash mobs as activism, to protest controversial development or raise awareness about a social issue.

The mob that menaced South Philadelphia Saturday appeared earlier this year - smaller in number and far less destructive - in University City at 40th and Walnut streets and Upper Darby, Bethel said.

Reached yesterday, Upper Darby Police Superintendent Michael Chitwood said in recent weeks there has been an increase in young people coming into the 69th Street area of Upper Darby via the El about 9 or 10 p.m. on weekends.

"The crowds have increased tremendously over the last two or three weeks," he said. "Guesstimates range anywhere from three to four hundred kids on Friday and Saturday nights."

Chitwood said many of the kids will line the streets and pack into the lobby of a movie theater there, refusing to leave.

"That number of young people walking back and forth certainly is threatening, looking at just the sheer numbers," he said.

"At this point we've had no major problems," he added. "At this point in time, we're in the vigilant stage."

In the city, besides monitoring social-media networks, Bethel said, police will beef up patrols this weekend in the area, collar curfew violators and disperse loiterers. Officers have also visited city high schools and talked with juvenile-court officials.

But he acknowledged that the spontaneous, anonymous nature of online social networking makes it difficult to counter when users employ it to agitate.

And social-media companies straddle a fine line when it comes to protecting the public while preserving privacy, said Susan Jacobson, an assistant professor of journalism at Temple University who studies social media.

"No [Internet] service provider wants to be a content cop. How would you notice a potential gang talking about potential criminal activity unless you were filtering for key words, which raises issues of privacy?" Jacobson said. "These entities do have procedures in place for monitoring potentially harmful content. But Facebook, for example, has 200 million users, so they can't monitor everything."

OurSpace, the new online network for the black community, launched in March, but already has more than 15,000 users, according to its Baltimore-based owner.

Applying a technological take to the adage "it takes a village to raise a child," Jacobson exhorted social-media users to alert authorities if they see criminal plots unfolding online.

"One of the people who follows these kids needs to develop some social responsibility" and report the troublesome posts, Jacobson said.

Parents also need to pay closer attention, she said.

"It's always good to know what your kid is doing, parents, if you can get on Twitter and Facebook, you can understand the electronic world your child is living in," she said.

And one resident suggested a novel way to turn social-networking into a crime-fighting tool: "We don't like Twitter because we think it is creating these crowds, but if a dozen people got $300 tickets for violating the noise ordinance, I bet they would Twitter to all their buddies about it and then the noise would stop."

Spokespeople for Facebook, Twitter and OurSpace could not be reached for comment. *

Staff writer Stephanie Farr contributed to this report.