A missing Royal New Zealand Navy sailor posted the last social media images of himself standing at the water's edge with "rough waves" crashing behind him, says his sister.

Joseph Tua has not been seen or heard from since last Saturday after he visited the area near To-Sua Trench, a famous tourist spot on Samoa's Upolu Island.

This is where Joseph Tua was seen in his last selfie shared with family and friends on social media. Photo / Supplied
This is where Joseph Tua was seen in his last selfie shared with family and friends on social media. Photo / Supplied

Tua, a junior sailor at the Devonport Naval Base who holds the rank of able stores accountant, flew to the Pacific nation on the morning of April 28 for a short holiday and to visit his two uncles, who live near Apia.

This morning, his sister, Isabel Tua, told the Herald her family and friends were searching through his Snapchat posts for clues as to what happened to the 24-year-old.

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"We managed to log on to his Snapchat and look at the most recent photos he had posted.

"There were lots of photos of him from Friday spending time with family, and then the last photo was of him standing near some rocks close to the edge of the water. There were some really rough-looking waves crashing behind him.

"It was from Saturday morning," she said of the last social media post. "It was a beautiful day and you could see the sun shining."

The family have declined to share the image publicly.

Isabel Tua, who travelled to Samoa with her sister and parents to help in the search, said her brother's bag, hat, iPad, wallet and passport were found near To-Sua Trench.

However, she said his cellphone was yet to be recovered.

Tua is described as an
Tua is described as an "adventurous boy that loves travelling and explore[s] unique places". Photo / Supplied

"He's always active on social media, and he wouldn't just leave these things behind like that."

She said Tua, who attended Auckland's De La Salle College and grew up in Mangere, had left his uncle's Samoan home on the morning of April 29 to explore parts of the island.

She said her family was coming to terms with the thought Tua may have died, and were now hoping to recover his body.

Jospeh Tua is a junior sailor at the Devonport Naval Base. Photo / Supplied
Jospeh Tua is a junior sailor at the Devonport Naval Base. Photo / Supplied

A member of a family who help maintain To-Sua Trench, a popular tourist spot and swimming hole, told the Herald when staff arrived on Saturday morning Tua's car was already in the car park.

She said Tua would've been the first guest on that morning, but staff and other guests did not see him.

On Thursday, a Samoan police constable familiar with the case told the Herald the investigation into Tua's disappearance was ongoing.

Police representative Su'a LeMamea Tiumalu told the Samoa Observer police were alerted when Tua's vehicle was found still parked near To-Sua Trench later on Saturday.

He said more than 20 police officers had been working on the case, including Police Commissioner Fuiava Egon Keil.

"We are working around the clock on this case," Tiumalu told the Observer.

Police on the island have also been assisted by the New Zealand High Commission in Apia, and the New Zealand Navy has sent a family liaison officer to Samoa.