GREELEY, Colo. -- Greeley police are looking for a teenage girl accused of attacking a runner in a city park last week.

Police said a 47-year-old Greeley woman was jogging in Glenmere Park at about 5 p.m. on Aug. 24 when she saw about 20 teenagers surrounding a girl who was beating up another girl.

The woman shouted at the girls to stop and threatened to call police if they didn't, according to the police report.

Several people turned around and started calling her a f***ing b**** and told her to mind her own business, Greeley police said.

The woman ran past them 20 feet and took her cell phone out of her pocket to dial 911, police said. That's when one of the girls shouted, "We're leaving now and I know you're calling the cops," according to the police report.

But another girl in the group yelled "F*** you, b****, rushed at her and punched her several times in the face, knocking her down to the ground, police said. The woman said the other girls in the crowd yelled, "Beat her up!" and encouraged the girl to attack the woman. Some even recorded the assault on their cell phones, the victim said.

The group scattered after the woman was knocked down, and the victim couldn't provide police a description of her attacker other than that it was a girl between 17 and 18 years old.

Two witnesses in the park corroborated the victim's story and added that the suspect was wearing a yellow T-shirt. They said the girls -- between 13 and 18 years old -- were wearing normal clothing, and nothing that looked gang-related.

The victim, who says she jogs at that park nearly every day, suffered cuts and bruises to her face.

Police are asking anyone who saw the attack to come forward. They are especially interested in seeing the cell phone video, if any was recorded.

Officers have sent an e-mail to school resource officers, asking them to be on the lookout for teenagers showing pictures of video of this attack on their phone.

Anyone with information is asked to call 970-350-9600 or 970-350-9605.

Because there's no detailed description of the suspect, police have classified this case as inactive.