Police investigating the 1993 killing of sex worker Jayne Furlong have been sifting through dirt at her former flat in South Auckland.

Officers and forensic experts spent Saturday investigating the soil that was dug up at the front of the property in Onehunga, Fairfax Media reported.

A tree and other shrubs were removed and material was bagged up and tagged "ESR" for further forensic investigation.

Ms Furlong shared the flat with her boyfriend, Danny Norsworthy, at the time of her disappearance.

Detective Inspector Mark Benefield said police were acting on information that required further investigation.

Ms Furlong, a part-time sex worker, was last seen by her boyfriend after he had dropped her off to work on Auckland's Karangahape Road on May 28, 1993.

The 17-year-old's remains were found buried in sand dunes at Port Waikato in May this year. Police have said they believe more than one person was involved in her death and are seeking a man known as "Tommy", who was entered in her diary around the time she went missing.