"That was a decision that they were trying to make on the Thursday, so we'd obviously like him located as soon as possible," he said.
"There's no reason for why he's vanished and until we probably speak to him, we can't fill in the gaps either," Mr Membery said.
"We can't really speculate that he's just run off, or it could be part of his medical condition which has made him disoriented, but that's another speculation."
Rotorua Boys' High School acting principal Fred Whata said Matthew had a health issue since he started at the school in Year 9.
"He has not been at school for terms two and three because of this," he said.
"Our Year 12 dean has been in contact with Matthew and his family and providing material for him to continue his schooling at home."
Mr Whata said Matthew was a very good student who was well-liked by his peers.
"If anyone has seen him I urge them to get in touch with the authorities."
Mr Membery said police were not considering foul play. He said possible sightings of Matthew had been followed up without success.