(CNN)The father of an 18-year-old Belgian backpacker who has been missing in Australia for more than two weeks broke down in tears as he appealed for help to track down his son.
Theo Hayez was last seen at 11 p.m. on May 31 at a hotel in Byron Bay, a coastal town popular with tourists, around a two-hour drive south of Brisbane.
Police say they have "serious concerns" for Hayez's well-being. Officers were informed of the teenager's disappearance on June 6, when he didn't return to his hostel.
Hayez does not appear to have made any financial transactions or used his mobile phone since he went missing, police said.
The teen's father, Laurent Hayez, said his son had used encrypted messaging service WhatsApp the night he went missing, and called on the company to disclose his son's messages.
"We know that Theo used WhatsApp the night he disappeared. We understand the politics about confidentiality and respect that," he told reporters on Monday.
"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."
A WhatsApp spokesperson told CNN the company was assisting law enforcement in accordance with the law and its terms of service.
Local police have conducted extensive land, air and sea searches around the town, and are continuing to request that anyone with additional information come forward.
"Even if you think the information may be small, it may be the missing link we need to find Theo," Superintendent Dave Roptell, the local district commander, said in a statement.
"We want to provide answers for his family both here in Australia and back at home in Belgium."