A land and air search failed to find the 27-year-old, who was last seen near Wilsons River, about 20km south of Noccundra, at 9.30am on October 18.
Mr Rivers' disappearance is now a criminal investigation and Southern Regional Crime Coordinator Detective Acting Superintendent Stephen Blanchfield will give more details at a press conference on Thursday afternoon.
His mother, Joanne Rivers, has set up a GoFundMe webpage to raise money for the search, with 151 people donating more than $12,500 so far.
Mr Rivers had been travelling back to Darwin from Balranald in the NSW Riverina after playing AFL when he went missing on a remote outback road near Noccundra, she said.
His grandmother, whose name has not been released by police, earlier this week begged him to come home and for anyone with information about Mr Rivers to come forward.
"Jayo, my heart is broken and so is the rest of the family ... please come home," she said in a video issued by police on Monday.
"Please go to the nearest police station, or keep yourself safe with prayers."
His grandmother described Mr Rivers as an outgoing man, one of eight siblings, saying it was out of character for him to not contact his family.
"Jayo, that's his nickname, is a role model to all his siblings, his younger brothers look up to him, his sisters respect him, elderly people respect him because of his nature. He's a good-natured young fella and we all love him so dearly," she said in the video.
"Please, if anyone out there has seen my grandson please call the police, let them know, we're so worried about him, we need him back home for Christmas."
Mr Rivers is about 185cm tall, has a slim build and a tattoo of a cross under his right arm.
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