(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.

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