Linda Frances Sidon, who had been living in the Gold Coast at the time of her disappearance, was last seen in June 2009 at the Ashmore home where she lived with her son Daniel.
Now Queensland police have begun searching bushland in the Numinbah Valley where they believe the body of Ms Sidon is buried.
The 46-year-old's disappearance went unreported for more than a year before her father raised the alarm with police in New Zealand in late 2010.
At the time Ms Sidon's history of anorexia, anxiety and depression led police to believe she had committed suicide.
But new information now has her disappearance being treated as suspicious.
Southeast police regional crime co-ordinator Detective Inspector Dave Hutchinson said there has been no proof of life since June 21, 2009.
He said the ongoing investigation has led to the strong suspicion Ms Sidon, a part-time cleaner, was murdered.
"The pace of the investigation increased recently," Mr Hutchinson said.
"We have been able to confirm that she has not left Australia, she has not gone back to New Zealand and all inquiries would suggest that she has not left the Gold Coast either.
"As a consequence of our inquiries, we believe that she has met with foul play."
Mr Hutchinson said police have several persons of interest in the investigation, including Ms Sidon's now 28-year-old son.
A search is underway near Pine Creek Road in Numinbah.
Cadaver dogs last week located several "locations of interest" which police were now excavating.
Police are urging any acquaintances of Ms Sidon to make contact with them.
- By Ed Jackson of AAP
