Police and the family of a Brisbane man who vanished with his motorcycle 15 years ago are appealing for help to solve his suspected murder.

The brothers of Brisbane man Gerhard Bruno Wagner have tearfully pleaded for information to help solve his suspected murder.

The 61-year-old and his motorcycle vanished 15 years ago.

Mr Wagner’s brothers, Paul and Peter Wagner, have never given up hope of finding out what happened and renewed a public appeal on Monday.

They say Mr Wagner wasn’t the type to disappear without saying goodbye, and they don’t believe he had enemies who wanted him dead.

He had lifelong friends, would lend money to mates in need and was a doting older brother and son, they said.

A $250,000 reward was issued two years ago but there has been no breakthrough.

Paul Wagner was visibly shaken as he appealed for fresh information.

“It is still very raw,” he said. “Not a day goes by that we don’t think of him.

“We need to give him a decent burial and start to heal from this terrible tragedy.”

Gerhard Wagner had worked as a merchant seaman and was building a boat to sail in his retirement.

He was last seen leaving his friend’s boat-building workshop in Hemmant near the mouth of the Brisbane River on his 1986 Kawasaki Virago 750cc motorcycle about 3pm on January 7, 1999.

Wearing paint-splattered blue overalls, Mr Wagner was intending to head home to Wooloowin before meeting a friend for dinner and was due to return to the workshop the following day.

But he didn’t turn up for either appointment and was reported missing 11 days later.

Over the years police have continued their search, including trawling waterways for his motorbike.

Detective Superintendent Steve Holahan of the State Crime Command’s homicide group said police have a “strong belief” he was murdered.

“You’ve got a motorcycle and a person, and they don’t go missing off the face of the Earth,” he said.

“We believe he met with foul play.

“We certainly believe someone has the key to what happened to Gerhard that day.”

Police have said that any accomplice who comes forward will receive indemnity from prosecution.