The search for Belgian teenager Theo Hayez, who went missing in northern NSW 11 days ago, has been narrowed down to two areas near the Byron Bay town centre through the use of phone records.
The 18-year-old was last seen leaving Byron Bay's Cheeky Monkey's bar about 11pm on Friday, 31 May, and has not been seen or heard from since.
He hasn't used his mobile phone or made any financial transactions since that time, NSW Police said.
Mr Hayez's mobile phone records have helped investigators narrow down the search area. Source: Facebook
But Mr Hayez's mobile phone records have helped investigators narrow down the search area to the east of the Byron Bay CBD and in and around bushland to the northeast.
"Our last recorded phone records indicate the phone was used in and around this area," Detective Chief Inspector Matthew Kehoe said in Byron Bay on Monday.
"We haven't located anything of significance thus far but our search continues ... It is a very unusual behaviour from Theo.
"He is usually very regular in the contact with his family, hence we do have concerns for his welfare."
Chief inspector Kehoe said one inquiry police were pursuing was whether Mr Hayez was with someone else when he disappeared.
"We believe that someone must have seen Theo after he left the licensed premises," he said.
Mr Hayez's belongings - including his passport - were found untouched at the Wake Up! Hostel in Byron Bay after staff raised the alarm when he didn't check out as planned.
He was supposed to travel to Melbourne before returning home to Belgium this week, according to a Facebook post by his friend Michael Dorkhom.
The search for Mr Hayez ramped up on Monday with police, the SES, the Westpac Life Saver Helicopter, Surf Life Saving and volunteer Marine Rescue all involved.
Alongside the search efforts of NSW emergency services, locals and backpackers alike have also been searching for the missing teenager.
Volunteers have met outside the bar where Mr Hayez was last seen since Saturday, covering the surrounding region and focusing on low frequented areas.
Anyone with information about this incident is urged to contact Crime Stoppers: 1800 333 000 or https://nsw.crimestoppers.com.au.
