The family of missing Belgian backpacker Theo Hayez says a leak to media that there had been a DNA development in the case is "deeply disturbing".

A report this week by Belgian news agency Belga claimed DNA testing of a cap found in bush by the Cape Byron Lighthouse suggested it belonged to Hayez.

If true, it would be further confirmation that Hayez's last movements were around Cosy Corner on the northern end of Tallow Beach, near the lighthouse on the night of May 31.

The official police theory is that the backpacker fell off cliffs near the lighthouse and into the ocean, but the family has disputed this.

In a statement posted to Facebook today, Hayez's family said they were outraged about the report.

"The fact that this information published by Belga came from a 'good source close to the file' is extremely shameful and demonstrates a complete disrespect for the family and the work of the Australian police," the family said.

"It is deeply disturbing."

There is no suggestion NSW Police or any other official outlet in Australia leaked the test results.

Belga reported the DNA results pointed to a "family link".

The cap, which bears the same description to one Hayez was wearing when he disappeared on May 31, was found in bushland in July during extensive searches by police and volunteers.

The cap was found in the lighthouse area, where the backpacker's mobile last "pinged" a signal on June 1.

Earlier this week, Hayez's family posted on Facebook that investigations were continuing and they had received the results of the DNA tests of two hairs on the cap, but did not say what the results were.

The family on Monday launched a fresh appeal for information about the disappearance of Hayez, who was last seen leaving the Cheeky Monkey's bar in Byron Bay on the night of May 31.

It said it was launching a new public campaign.

"It will soon be one year now and it is still important that you keep talking about Theo, we still believe that someone out there could help us to find out what really happened by providing us with some information about that night," the family said on Facebook.

The police investigation was formally closed in September and the matter referred to the coroner.