At the end of the 1.07-minute video, the girl collapses by the roadside.
The Facebook posting comes with an introduction which says, "Ok everyone so over in Christchurch there has been a 4 on 1 beating that has caused lots of drama in Christchurch. Poor thing, she didn't even want it she was dragged into it! Like to support the poor girl."
It has received almost 8000 likes, and has been shared 2,300 times.
The page was set up by 14-year-old Jayvin Ryder.
He posted the video after seeing it being shared with some of his online friends.
"What I was trying to achieve for this was to stand up for her and make sure nothing else happens," he told 3News yesterday.
"What I want to do is get everybody in a big group and help her really, because everyone who gets bullied shouldn't be."
Police received a complaint and a copy of the video.
"We have positive leads as to the identification of the alleged offenders," a police spokesman said today.
There are four females aged between 12 and 16, he said.
"We are making inquiries to locate and speak to them."
They have not been spoken to and inquiries are continuing, the police spokesman said.
The 14-year-old victim is recovering at home.