Associated Press

LOS ANGELES — Packs of young people rampaged through Hollywood, knocked down people and stole cellphones and other items before a police sweep halted the marauding and arrested a dozen people, police said Wednesday.

Calls began coming in at around 8:30 p.m. Tuesday that youths were robbing people and stealing T-shirts and other goods from businesses, mainly on Hollywood Boulevard, Lt. Ray Valois said.

Fifteen to 20 young men and women were "attacking victims and taking property," he said. "Some people may have been knocked down or punched."

However, no serious injuries were reported.

As many as 40 people may have been involved, splitting into smaller groups and reforming as they looted people nearby, Valois said.

Surveillance video aired on television showed youths roaming along the famed Hollywood Walk of Fame.

Several people told journalists that they were surrounded by groups of youths that forced them to hand over cellphones, a watch and other items.

"I was filming celebrities coming out and all of a sudden I was approached by this group of people and one got my phone," Lori Aceves told KNBC-TV. "And all I know is this lady next to me — I have no idea who she was — but she grabbed me by the arm and she tucked me in and she moved me to a different store."

Her iPhone and other stolen items were later found in a backpack, the station said.

More than 100 police officers were called in and most arrests were made within five minutes, but officers swept the area for about an hour before the operation was completed, Valois said.

Twelve people — all but one under the age of 18 — were arrested and none lived in Hollywood, he said. Eleven were held on suspicion of robbery and one for receiving stolen property.

It appeared that the attackers were loosely organized through social media, including some Web messages urging people to gather in Hollywood "to riot," Valois said.

The attacks followed the arrests of 14 people a night earlier in the city's Crenshaw District after about 150 people ran through the streets, jumped on cars, tried to break store windows and punched bystanders. A Wal-Mart store was vandalized. Police said that group split off from a peaceful protest over George Zimmerman's acquittal.

It was unclear whether the Hollywood marauders were inspired by either that violence or anger at Zimmerman's Florida acquittal for the shooting of Trayvon Martin.

"None of these individuals was protesting, there was no physical evidence of that," Valois said. "They may be acting out."

The area may have been chosen because "Hollywood's open late, there's a lot of people here, we get a lot of media attention here," Valois said.

"I would not allow this to discourage any tourists or anyone coming to Hollywood Boulevard," he said. "I still believe it's a safe place."

Two protests Tuesday night in the Crenshaw District and downtown were peaceful.

Copyright 2013 Associated Press