Donny has not been seen or heard from since leaving the River Track campsite, where he was staying with his sister, Rachael O’Keane, and friends.

Rachael said she has been at pains to work out what happened to her younger brother who she last saw walking into bushland near their camp site. She said she and her family have spent every moment of the 13 months and 13 days since living in hope.

"It's the only thing that keeps us going," she said.

"Without that we would just crumble and not keep going on. My family has stayed devoted to finding Donny and we will never give up until we know what has happened to him."

Rachael said it was hard to accept there had not been one credible sighting of him.

Reports in the weeks after his disappearance suggested he may have been heading through Bendigo, or may have hitchhiked to Swan Hill.

With his 17th birthday passing earlier this year there were no further updates. His family have been at home in Ballarat waiting for any news or tip-offs that might help track him down.

"We have so many unanswered questions," Rachael said. "I wish I could say the longer time passes it gets easier but it doesn't it actually gets harder to understand why my brother has not been seen for a year. Someone must know something and after all our efforts to find Donny it feels like an unanswered prayer everyday that we don't get any information on Donny."

"There really aren't words to explain the heartache we have felt without Donny in our lives."

Anyone with information can contact Crime Stoppers on 1800 333 000.