It happened Tuesday around 3 p.m. at Pico Park off Beverly Boulevard.
The Los Angeles County Sheriff's Department said the suspect allegedly grabbed the girl's arm and pulled her as she walked through the park.
A Good Samaritan intervened and threatened to call police, authorities said.
That's when the suspect let her go, but not before authorities said he allegedly reached for a child that was with the Good Samaritan, but was unsuccessful. He ultimately took off running and remains on the run.
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The suspect is being described by authorities as a Hispanic man between 30 and 35 years old.
He's reportedly 6 feet tall and weighs 200 pounds, according to authorities.
The sheriff's department said he has "salt and pepper shaggy hair" and was last seen wearing a black sweatshirt with black pants and tattered shoes.
Anyone with information is encouraged to contact the Pico Rivera Sheriff's Station at 562-949-2421.