Key Points:

A man who sexually assaulted a schoolgirl in northwest Auckland last week after posing as a truancy officer may have not have been a local, police say.

The man pulled alongside the 15-year-old girl in Hobsonville Road around lunchtime on November 11 and told her he had to drive her home to ensure she wasn't wagging school.

At her house he waited until she opened the door before sexually attacking her.

Detective Sergeant Steve Salton from Henderson CIB said the offender - a short, stocky Maori or Polynesian man aged about 40 - was probably not a local as he didn't know the local roads well.

"He knew Hobsonville Road but not the rest of the area. He needed directions from the girl to some of the main roads in the Hobsonville area," Mr Salton said today.

"She said that at the time she thought it was a bit strange but not suspicious."

Though he was apparently not a local, he could easily have been from another part of Auckland or even another part of the country.

Mr Salton said police were investigating "more than 100" possible suspects that had been reported to them.

"At the moment we're going through the process of eliminating who we can and making more enquiries for those that we can't," he said.

"There's a lot of work to do."

Mr Salton said the man's vehicle - a white station wagon with a tidy, light grey interior - had not been seen in the area since.

Police had also been unable to locate the girl's backpack and mobile phone, which were taken by the offender. The mobile phone has not been used since it was stolen.

"If we find the person hopefully we'll find the car and the other items."

The man may have received scratches on his neck from the attack after the girl put up a fight.

Mr Salton said the girl was currently focusing on her NCEA exams and had received great support from her family.