Police say they hold concerns for a Belgian backpacker who has been missing for a week in Byron Bay.

Key points: Theo Hayez was reported missing on June 6

Theo Hayez was reported missing on June 6 He was last seen leaving a Byron Bay bar on May 31

He was last seen leaving a Byron Bay bar on May 31 He used WhatsApp early the next morning but has not answered his phone

Theo Hayez, 18, was reported missing by staff at the WakeUp! Backpacker hostel yesterday, after he failed to check out of his room.

Mr Hayez was last seen leaving the Cheeky Monkey's bar about 11:00pm on May 31, wearing a black hooded jumper, beige pants and black shoes.

He had been active on WhatsApp in the early hours of June 1, but had not been heard from since.

Chief Inspector of Byron Bay Police, Matt Kehoe, said his disappearance was "out of character".

"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," he said.

"Certainly from our inquiries, we do have concerns."

Mr Hayez arrived in Australia late last year on a working holiday visa and was due to fly home to Belgium just a week after his disappearance.

'He wouldn't have changed his plans'

Family friend Michael Dorkham said he'd seen Mr Hayez two weeks ago, and he discussed his plans 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."

Theo Hayez was seen leaving Cheeky Monkey's bar alone on May 31. ( Supplied: Cheeky Monkey's )

Mr Dokham said his friend was last seen leaving Cheeky Monkey's 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."

Inspector Kehoe said police were scouring CCTV footage of the Byron Bay area and were monitoring his social media, and bank accounts.

They were also liaising with the Belgian consulate and were in regular contact with Mr Hayez's family, he said.

Mr Hayez is described as Caucasian, about 180cm tall with a thin build, blue eyes and blonde hair.

WakeUp! backpackers declined to comment on the disappearance.