Missing Belgian tourist Theo Hayez (R) was seen in a shop in the coastal tourist town of Byron Bay, Sydney on May 31, 2019. AFP

The father of a teenaged Belgian backpacker missing in Australia for more than two weeks pleaded for help on Monday, saying his son could be in grave danger, as police called the disappearance baffling.

Theo Hayez, 18, vanished after leaving a bar in Byron Bay, a holiday town 765 km (475 miles) north of Sydney, late on May 31. He has not been seen or heard from since.

“This is a question of providing assistance to a person in grave danger,” Laurent Hayez told reporters in Tweed Heads, 66 km (41 miles) north of where his son was last seen.

“We know that Theo used WhatsApp the night he disappeared,” he added, appealing for help to access the messages sent in the hours before the disappearance, but without saying why he believed his son to be in danger.

Police, notified of the disappearance on June 6 after Hayez failed to check out of his hostel and could not be found, said they had narrowed the search to two areas near the centre of Byron Bay, based on his last telephone records.

Hayez had been backpacking around Australia since November and was due to return to Belgium last week, media have said.

Police said they had few clues and added that they had asked Whatsapp's owners, Facebook, to help, but it would be quicker if other group members provided access to the messages.

Facebook did not immediately respond to requests for comment.

Reuters