The father of a missing Belgian backpacker has made an emotional plea for information as homicide detectives join the search effort in northern NSW.

Key points: Theo Hayez was last seen in Byron Bay on the night of May 31 leaving a bar

Theo Hayez was last seen in Byron Bay on the night of May 31 leaving a bar His father has travelled to Australia to make a public appeal for clues

His father has travelled to Australia to make a public appeal for clues Police say they are "baffled" by the 18-year-old's disappearance

Theo Hayez's father, Laurent Hayez, broke down as he pleaded for public information about his son's disappearance, saying the 18-year-old was "in grave danger".

"When I left Belgium I promised Theo's little brother, Lucas, I would bring his brother home, please help me keep my promise to him," he said.

Theo had been in the popular tourist town of Byron Bay for less than 24 hours when he disappeared after leaving the Cheeky Monkey's nightclub at around 11pm on Friday, May 31.

"We know that Theo used WhatsApp the night he disappeared," Mr Hayez said.

"We understand the politics about confidentiality and respect that.

"However, this is a question of providing assistance to a person in grave danger.

"It is vital that investigators get access to Theo's WhatsApp account without delay. Every minute counts."

In a statement WhatsApp said it was working with police.

"We understand the important work being carried out by law enforcement and are assisting them in accordance with applicable law and our terms of service," a spokesperson said.

'We are baffled'

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 55 seconds 55 s CCTV footage of missing backpacker Theo Hayez

NSW police were notified of Theo's disappearance when hostel staff found his belongings, including his passport, in his room, but realised he had failed to check out.

SES crews, the dog squad, lifeguards, local volunteers and police are continuing to search the Byron Bay headlands, east and north of the town, as well as beaches and swamps.

Rescue teams have also searched the Cape Byron area, where his mobile phone was last "pinged" on June 1, 2019.

But so far, there has been no trace of him.

Belgian backpacker Theo Hayez was due to fly home in early June. ( Supplied )

A NSW Police spokesperson said they were not able to rule anything out and that "there's no indication at the moment of which way the search is going".

Detectives have released new CCTV footage showing Theo at a convenience store about 7.45pm on the evening he disappeared.

"We are baffled. We are baffled because that is all we have," the spokesperson said.

Mr Hayez thanked those involved in the search effort.

"I would like to thank his cousin and his godfather, who since it was discovered that Theo was missing, have been searching for him," he said.

"I would like to thank the Byron Bay community and all Australians for their welcome, logistical support and their lovely kindness.

"Thanks also to SES and all the volunteers who have been searching for him."

In a statement, WhatsApp said it was working with authorities.

"Our hearts go out to Theo Hayez and his family," the statement said.

"We understand the important work being carried out by law enforcement and are assisting them in accordance with applicable law and our terms of service."