Police have released CCTV footage of missing French man Eloi Jean Rolland, 18, at Auckland's Britomart train station.

The family of missing teen Eloi Jean Rolland are desperate for answers as they start to lose hope of finding him alive.

The French exchange student, 18, had been living with a host family in Auckland's Birkenhead since he arrived in New Zealand in September.

On March 7, Rolland caught a train from the Britomart Station in the CBD about 6.30am and exited at New Lynn's Fruitvale Rd station about 7.26am.

Police believe he may have walked from there to Piha, on Auckland's rugged west coast, as mobile phone data indicates he was in the vicinity of Piha Rd at 9.18am.

READ MORE:

* French national Eloi Jean Rolland 18, missing in Auckland

* CCTV footage of missing French man released as concerns for him grow

* Search and rescue teams hit Auckland's Piha in search for missing French man

* Missing French teen: Residents in Piha asked to check vacant properties

* French teen missing from Auckland had 'troubled' state of mind

The teen, who has limited English, has not been seen since he was captured on CCTV at Britomart over three weeks ago.

Search and rescue teams have been searching the wider Piha area since March 17 and requested residents check their homes and any unoccupied properties for any sign of Rolland having been there.

Supplied Rolland's sister Aurore described him as "fit and smiley".

Police are in daily communication with Rolland's family, who are unable to travel to New Zealand from Montpellier in France due to borders being closed to non-residents because of the coronavirus pandemic.

Speaking from Paris, Rolland's sister Aurore told Stuff the family is desperate for an answer on his whereabouts.

"We have no insight. We are starting to lose hope to find him alive."

They are particularly worried that his phone has stopped emitting data, she said.

The family believes the last person from France to hear from Rolland was a friend on March 4. The pair had discussed plans for when Rolland returned to France on March 8 due to feeling homesick.

Supplied/NZ Police Rolland was last seen on CCTV footage at Auckland's Britomart train station on the morning of March 7.

"He has no suicidal intention," Aurore said.

Rolland had made some friends at his language school in Auckland and the family had seen people communicating with him on social media. The family had also been in contact with his roommate.

He had recently expressed an interest in hiking.

"He is fit and healthy. He was a sailing instructor so he is really athletic," Aurore said.

"[But] I don't know how someone [can] hike for 20 days."

Supplied/NZ Police Eloi Jean Rolland came to New Zealand from France as a foreign exchange student in September 2019.

Other than the police, who had been keeping the family in the loop regarding their investigation, Aurore said "we are on our own".

"We hope someone will see him or any items of interest.

"You can't miss him. He is French, fit and smiley."

The family previously said Rolland's disappearance was "very out of character".

They described him as a "calm, kind and curious teenager who loves adventures" in a statement.

"He loves the sea, surf and catamarans. He also enjoys the beauty of the wilderness.

"We are extremely worried. He has never run away from home and always stayed in contact with his family.

"We are forever grateful to the New Zealand public for your support and assistance at this very difficult time for our family."

Police continue to have dedicated staff looking for Rolland, despite the coronavirus lockdown, a spokesman said.

"Unfortunately there have been no recent sightings of Eloi however Police continue to assess information from members of the public.

Police are keeping an open mind as to what has happened, however there is no information at this stage to suggest the matter is suspicious."