"Police would like to ask everyone who has shared this video to remove the post and stand up to oppose violence in our community.
"If you share it, you're no better than the people who commit this behaviour," he said.
Mr Swann said a 15-year-old girl had been arrested and charged with assault. She appeared yesterday in the Kaikohe Youth Court.
"It was a very serious assault," he said.
The victim had suffered head and facial injuries. She and her family were upset and shaken by the "vicious, unprovoked attack".
Mr Swann thanked people who went to the victim's aid but was concerned that many watched and did nothing.
In the video a girl is repeatedly kneed and punched by a larger girl for about two minutes. A teenage boy approaches but does nothing to stop the attack, which ends when adults intervene.
Many people, including schoolchildren on a bus, saw the attack at the Mangakahia Rd bus terminal. Police patrols had been increased around the bus drop-off area to prevent more trouble.
Cyberbullying or posting material on social media to harm people is not illegal at the moment, but that will change when the Harmful Digital Communications Bill comes into law. That will create an offence punishable by up to two years' jail or a $2000 fine.
The accused's Facebook page was inundated with threatening and abusive messages yesterday, as well as comments defending her or calling on others to leave her alone.
It is understood she was in CYF care. Police would not comment on where she was from or the school she attended.
