"I cannot discuss the details of the investigation for privacy reasons. We have taken this situation very seriously and have been working with the police from the early stages."
She said the school had "processes to support investigation that are robust and fair".
Police would not comment on the case, but a spokesperson said bullying could cause serious harm to victims and where necessary, further action may be taken by police.
"We encourage young people to talk to a trusted adult, such as a parent or a teacher, or to talk to Netsafe.
"Under The Harmful Digital Communications Act, Netsafe offers a free service for people in New Zealand to help with online bullying, harassment and abuse - it is available seven days a week on 0508 NETSAFE (0508 638 723).
"As a precautionary measure, police encourage young people to ensure they are cautious about personal details provided online and regularly change their passwords.
"Most social networking sites including blocking and unfriending people and reporting content. Additionally, phone numbers can be blocked on your phone where necessary."