Detective Senior Sergeant Mal Hassall said the incident was disturbing, given the man was aware the girl's mother and shop staff were near.
"This a very concerning incident where a male has brazenly followed the 14-year-old girl into the changing area, despite her mother and a staff member being close by.
"I'm very concerned by this type of offending,'' Hassall said.
"This was very disturbing behaviour and we need anyone who knows who this man is to contact us.
"He drives a very distinctive white car with a black driver's door - someone will know this car and will know this man's identity.''
The man involved is described as being of Maori or Pacific Island descent, aged about 25 to early 30s.
He is of solid build and was wearing a dark grey/brown hooded jersey, black shorts and black shoes.
• Do you know this man? Anyone with information is urged to contact Police on (09) 295 0200 or CrimeStoppers anonymous: 0800 555 111.