A $5000 reward has been offered to anyone who can confirm the South Island kōkako is still alive.
The South Island Kōkako Charitable Trust, which is offering the reward, said it would be paid once experts confirmed any evidence provided did indeed confirm the bird still existed.
The bird had been listed as extinct until 2013 when credible sightings prompted it to be reclassified.
But there is still no confirmation it exists.
Trust chair Dr Euan Kennedy said if the kōkako did exist there would only be a small number alive and it was important they were located so work could be done to ensure their survival.
"In this search we are attempting something quite new for New Zealand. We are passionate to find evidence of the kōkako's survival in the native forests of the South and Stewart islands. To our knowledge no Trust has pursued a quest such as this."
The North Island kōkako, which has a blue wattle, is mainly restricted to pest-controlled areas. The population has increased to about 3000 from just 660 at the turn of the millenium.
Dr Kennedy said the trust wanted the public, bird watchers and other backcountry user to be its eyes and ears in the southern forests.
"Kōkako calls are so distinctively different they will stop you in your tracks. Even so, the song of a tui is known to sound very similar.
"Sound recordings have yet to provide the evidence we need. That's why we're appealing to birders and backcountry users to find more convincing signs of the birds," he said.
The Trust is inviting people to record possible encounters with the bird through its website.