Police vowed to deploy more officers to South Philadelphia after hundreds of teens, notified through online social networks, flocked to the city early today and created mayhem along South Broad Street.

"It's kind of a new dynamic that's growing, with large groups of juveniles using the social networks to get out the word," said Lt. Frank Vanore, the department's spokesman. "We're not going to tolerate it."

A group of teens on foot hijacked a taxi at 12th and South Street after getting into a confrontation with the driver and drove the vehicle into a tree at 12th and Fitzwater. Two passengers were injured slightly, police said.

Other youths pulled a woman and her passenger from a Jeep and assaulted them and stole the driver's purse. The driver is a paralegal from the Philadelphia District Attorney's office, Vanore said.

Maurading teens, most between the ages of 14 and 17, also vandalized a Sunoco convenience store at Broad and Catharine Streets, he said.

Several juveniles were charged with violating the midnight curfew, Vanore said, but none were arrested for the more serious incidents.

Vanore said the teens apparently were communicating through online networks such as Myspace and Twitter. He said police were working to monitor the networks.

He said police had noticed groups of teens converging on the city in the last few weeks, but today's gathering was substantially larger and overwhelmed law enforcement. "With a big crowd, there's nothing you can do," he said.

"We're looking at the incidents," Vanore said. "We're going to deploy more resources up there."