Fisherman Trent Riley posted two videos on social media showing calm waters two hours before he went missing off the coast of Brisbane.
The 26-year-old's small aluminium boat was found empty and motoring in circles off Mud Island, near the Port of Brisbane, at about 3.30pm on Wednesday.
Police Acting Inspector Mark Mooney says Mr Riley posted two videos on Instagram at 1.27pm which showed calm conditions on the bay.
"That's the last we heard of him, of his posting or interaction," he told reporters on Thursday.
Insp Mooney said the boat was not damaged, indicating there had not been any collision, but one of the 26-year-old's three fishing rods was missing.
He said a dry bag Mr Riley would have taken with him if he had "voluntarily" got into the water was still in his boat.
"No, we're not totally aware at this stage how he's fallen out of the boat," Insp Mooney said.
Water Police, Volunteer Marine Rescue, helicopters and volunteer coast guard have now been searching for Mr Riley for almost 24 hours.
Insp Mooney said Mr Riley's family have also started their own search.
"I just spoke to his mum, she's obviously holding out hope, as we all are," he said.
"It's been 24 hours, she's aware survivability after 24 hours is quite low, which is very heartbreaking for her family and friends.
"However, she's holding up the best she can, the best that anyone can expect in the circumstances, and we're still really holding out hope that we can bring him home alive to her."
At the time he went missing Mr Riley was wearing a long-sleeved grey fishing shirt, black jeans, black shoes and a bucket hat.
He is Caucasian, about 183cm tall, with a proportionate build and brown hair.
