Surjit Takhar, 37, was reported missing from his home in Oldbury, West Midlands, in October 2008.
His skull and other skeletal remains were discovered near the M54 in Telford, Shropshire, last August by maintenance workers.
The cause of his death remains unexplained but detectives are treating it as murder.
See more stories from Birmingham and the Black Country here
His family - including son Harry, 21, and 22-year-old twin girls Sohnia and Sohnay - have joined detectives in launching a fresh appeal for information about the case.
Mr Takhar's ex-wife Lavina Sohl said the family "need justice".
She said: "We just need answers.
"There must be someone who feels guilty, somebody knows something."
Mr Takhar's brother-in-law Jasvir Sohl said the family was "heartbroken".
Det Insp Jim Munro from West Midlands Police said: "We particularly want to speak to someone who called police in January this year saying they had information about Mr Takhar, but the call was cut off before the caller's name could be taken.
"I would urge that person to contact us again."
The family of a man who disappeared eight years ago have issued a fresh plea for information.