Police said they were aware of the footage and confirmed the assault happened outside a school in Counties Manukau South.
Pukekohe High School principal Richard Barnett said the school's senior management identified the teenagers involved and sent their names to the police. However, he said the people in the video were not students of Pukekohe High.
The attack happened outside the grounds of Pukekohe North Primary School. The students were not from that school either.
Pukekohe North Primary School principal Jim Stafford-Bush said: "The school believes they are likely to attend the local high schools and are hopeful the school concerned will address the conduct of these students."
Counties Manukau South Area Commander Inspector Joe Hunter said: "We are very concerned by the violence shown in the video and ask the community to cease sharing the video any further."
He said police were following positive lines of inquiry and were working with their partner agencies to address the violence in the video.
A friend of the girl being beaten up in the video said it was hard to explain how the victim in the video was feeling after being "on blast all over social media without people even thinking how it makes her feel".
"It should have been censored. She is traumatised and I hate how this will impact the whole world who comes across this disgusting video because we're all not like this.
"But imagine coming home from school to three girls attacking you for something you had no control over.
"I have never seen my home town like this; we all have a lot of love for each other. It breaks my heart that this poor girl has to fear being seen again because girls thought it was okay to do this to her.
"She also doesn't know who's out to get her next because of how viral the video is going."
