Staff noticed the Marlborough green gecko, known as Graham, which has lived at the Fiordland National Park Visitor Centre for 30 years, was missing from its terrarium on Wednesday.
The padlock to the terrarium was missing and marks on the latch pointed towards it having been forced or cut. Doc operations manager for Te Anau Greg Lind said it was distressing to think the animal, that had lived in one place all his life, might be subjected to uncomfortable experiences.
"The gecko has a distinctive grey mark on its head and would be easily identified. It’s our longest serving advocacy animal in Fiordland, and staff just want it back safe.
"It has outlived another gecko which used to share its terrarium.
"The police have been notified, and we are asking everyone to keep their eyes open."
The terrarium is near the entrance to the Fiordland National Park Visitor Centre, meaning all visitors to the area get to see him.
The terrarium was refreshed with food and leaves mid-afternoon on Sunday.
When the ranger returned three days later, the padlock had been removed and the gecko was missing, Mr Lind said.
Senior ranger Kate Hebblethwaite said staff were "just devastated" by the apparent theft.
She was aware geckos were an attractive item on the black market, but said she "could not speculate" as to what might have happened.
"I am not sure what would possess someone to do something like this," she said.
The Marlborough green gecko, also known as the manuka gecko, is endemic to New Zealand. The gecko, which can grow up to 70mm long, is classified as an "at risk" species.
Anyone with information about the missing gecko should contact Te Anau police or the Te Anau Doc office (03) 249-0200.
