Ryder August said her brother, Vincent Taurima, had saved her life when she was diagnosed with Leukemia in 2012.

Vincent Taurima was sitting next to a fire when he rang his father to tell him: "I don't think I'm going to survive another night."

The 21-year-old had already spent a cold night in Tongariro National Park, and was facing another, when he made that final call.

That was 17 days ago. Taurima and his friend Hākopa Ngaronoa​ had become lost in the bush on a track off Tree Trunk Gorge Rd.

ROBERT STEVEN/STUFF Hanging from a rope, the NZ Police's national dive team were taken to Tongariro National Park tributaries that cannot be accessed by land to search for two missing men.

His sister Ryder August is now pleading for the search to continue.

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Police warned on day five that hope was diminishing, and by day 12 it was said it would take a miracle for the men to be found alive. Since then searches have been scaled back.

SUPPLIED The family of Vincent Taurima.

But August still believes her brother is alive.

"The search has kind of come to a halt. There was momentum there but it's just – I don't know – dwindled off," August said.

"We just want to put the message out there that these boys are still missing, and any help offered would be greatly appreciated."

ROBERT STEVEN/STUFF A police dive squad joined the sixth day of the search.

The pair had fled police after refusing to stop in their stolen car on State Highway 1 about 3pm on Saturday, August 12.

They careened down Desert Rd before ditching the car, and evaded police by seeking refuge in the bush.

The first the family knew of this was after Vincent phoned them on the Saturday evening.

August has shared the words of his final phone call as she pleaded for searches to continue.

"They had a fire going, and the last communication was on the Sunday. That was between my brother and my father. My brother stated he didn't think he was going to survive another night," she said.

"It was quite disheartening to hear."

August said the call hammered home how serious the situation had become. That was over two weeks ago.

She was thankful to everyone who helped in the search, but with police, search and rescue, and volunteer searches kept separate, she said the family were left with a lot of questions.

"It just makes us feel like we've been abandoned, ignored," she said.

"My parents are still in Turangi at the moment, a lot of our family members have had to return to their lives to sort out and reintegrate back into their own world. That has put another halt on things."

But she said the family would keep searching.

"My parents are adamant to stay there and not come back home until they're recovered [my brother], what ever that may mean."

August said it now felt like a missing persons case, but Vincent had saved her life before, and now she was determined to do the same.

When she was diagnosed with Leukemia in 2012, Vincent was August's reason to keep fighting.

"It's different being on the other side. He was with me during a rough time when I didn't know if I was going to live or not."

"He had a heart of gold and a beautiful nature. From the public eyes, from the outside, he was quite off-putting, for some. Really he was genuine, beautiful."

A rāhui has been put in place to restrict use of the area, a cultural protocol led by Ngāti Tūwharetoa, and will be lifted when the iwi deem it appropriate.

But while August respects the intention, she said it was just another sign that others were giving up on the two young men.

"It's bigger than two lost men – it's like two lost families."