Mr Tascas, 27, from Whittington in Geelong, went missing some time between October 7 and 10, 2005.

His roommate Lawrence Butler was tried for his murder and sentenced to 23 years in prison in 2009.

However, his conviction was quashed on appeal two years later and in 2013, he was re-tried for manslaughter and found not guilty.

At the time of his disappearance, Mr Tascas was living at a home in Thatcher Court at Whittington.

He had sporadic contact with his mother, Pamela Tascas, but she became increasingly concerned when she did not hear from him for weeks, and reported him missing on April 1, 2006.

Investigators believe Mr Tascas got into a dispute with his roommate before he disappeared.

After he went missing, a number of his possessions including a vehicle and furniture were sold off, and his dog was given away.

His bank account showed a number of withdrawals in July and August 2006, and his phone was last used on October 7, 2005.

Mr Butler's girlfriend Jodi Harris was charged in July 2008 with being an accessory to manslaughter and obtaining property by deception.

She was sentenced to three years in prison in 2009.

Investigators believe there are still people who have key information in relation to Mr Tascas' death, prompting the $1 million reward.

After 16 years, police still strongly believe Mr Tascas was murdered, missing persons squad Detective Acting Inspector Tony Combridge said.

"While two people have previously been charged in relation to Trevor's suspected death, no one has directly been held to account for his murder," Det Insp Combridge said.

"It is a unique set of circumstances. However we believe there are still people out there who can assist us with this case and with providing Trevor's family with some level of justice."

Many of Mr Tascas' former associates still live in Whittington, where he was well known.

"While Trevor had his personal struggles, he was much loved by his family and they are still grieving his disappearance," Det Insp Combridge said.

"Hopefully this appeal will help detectives move the investigation forward and provide them with the answers they've waited so long for."

Australian Associated Press