Encrypted messaging service WhatsApp says it is working with authorities to help them locate missing Belgian backpacker Theo Hayez.
The 18-year-old's distraught father had earlier pleaded for access to his son's account believing it could hold the key to his whereabouts.
NSW Police admit they are "baffled" by the disappearance of the young man, who was last seen leaving the Cheeky Monkey's bar in Byron Bay about 11pm on May 31 after earlier being captured on CCTV buying alcohol in a bottle shop.
His father Laurent Hayez arrived in the country last week and on Monday appeared at Tweed Heads police station to beg the public for help, saying his son was "in grave danger".
"I promised Theo's little brother that I would bring his brother home. Please, help me keep my promise to him," Mr Hayez asked through his tears.
"If you have any information and if you do not want to deal with the cops, or if you are afraid to come forward, please make an anonymous call to Crime Stoppers."
Theo used encrypted service Whatsapp the night he disappeared and Mr Hayez asked for help in obtaining access to the messages.
"We understand the politics about confidentiality and respect that - however, this is a question of providing assistance to a person in grave danger," he said.
WhatsApp is providing information to law enforcement, but are limited in what data it can access from Theo's encrypted conversations.
"WhatsApp cares deeply about the safety of our users and our hearts go out to Theo Hayez and his family," a spokesman told AAP on Monday.
"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."
WhatsApp is only able to access and disclose some information which can include a user's name, last seen date, IP address and basic information but not the content of messages.
Theo had been preparing to return home after eight months travelling around Australia.
He was reported missing on June 6 when he failed to return to his hostel and couldn't be contacted. His passport and other personal belongings had been left untouched in his room.
While homicide detectives are helping the investigation, along with Belgian authorities, Superintendent David Roptell said he held out hope that Theo was alive.
"We're just not clear at this point," he said.
"It appears to be out of character. He was intending to go home. It's baffling as to what's occurred, but we're not ruling anything out."
Mr Hayez thanked police, volunteers and the community for their help in looking for his son, as well as those who raised money to support the search.
He said any crowdsourced funds not used to find Theo will be donated to a charity in Australia and Belgium dedicated to finding missing people.
Supt Roptell said it was "heartbreaking" that investigators did not have any fresh leads to share with Theo's family but promised not to leave any stone unturned.
© AAP 2019