An "astounding" number of people have come forward claiming someone they know may have killed Auckland teenager Tracey Patient.

But it's 40 years since her murder and her killer remains unknown.

Police re-opened the cold case investigation on the eve of the 40th anniversary in January and received hundreds of calls, but after investigations that included detectives travelling to Australia to follow up leads, the case has been wound down.

Thirteen-year-old Tracey was just five minutes from her parent's Henderson home, on her way back from a friend's house, when she disappeared on January 29, 1976.

A dog walker discovered her body, strangled by a pair of pantyhose, a day later.

Detective Inspector John Sutton said hundreds of theories and a number of leads were explored.

"It has also been quite astounding the number of people who have provided us with the names of people close to them who they suspected might have been involved," he said.

A number of people also contacted police about the number 126040 - a detail given to police by a mystery caller 22 months after Tracey was killed.

"The investigation has been progressed, but unfortunately it has not resulted in anyone being arrested and charged with Tracey's murder," Det Insp Sutton said.

Tracey's family are understood to be disappointed by the decision, but appreciative of police efforts to find her killer.

While it won't be actively investigated, the case will remain open if new information comes to light.