He was wearing a black hooded jumper, beige trousers and black shoes. Although he had been active on WhatsApp in the early hours of Saturday 1 June, no one has heard from him since.
Chief Inspector Matt Kehoe of the Australian police to the Australian public broadcaster ABC that Théo Hayez’s disappearance was "out of character".
He added that "We've spoken to some family members and he's normally very punctual in response to social media posts and we haven't got any of those since that time which is of concern to us and the family. Certainly from our inquiries, we do have concerns."
Théo Hayez arrived in Australia late last year on a working holiday visa and was due to fly home to Belgium next week.
“We are pretty concerned”
Speaking in an interview with ABC Michael Dorkham, who is a family friend, said that he had seen Théo Hayez a couple of weeks ago. Théo had told him that he planned to travel from Byron Bay to Melbourne before flying home.
"We're pretty concerned obviously, it's been seven days and no one knows where he is really. The fact that all his stuff is still at the backpackers is really concerning. We're doing everything we can, we've shared this all over Facebook and the community has been great, but we don't know more than that at this point", Mr Dorkham told ABC News.
Mr Dokham added that his friend was last seen leaving the Cheeky Monkey's bar alone and would not have changed his plans without telling anyone.
"We were talking about this a couple of weeks ago and he was telling me how everything he does needs to have been planned and he's definitely not the type of guy who would've done that."
Meanwhile, the police are scouring CCTV footage of the Byron Bay area and are monitoring Théo Hayez’s social media, and bank accounts.
The Australian police are also liaising with the Belgian consulate and were in regular contact with the missing teenager’s family.