Bruce Gapper vanished from his Dewsbury Moor home in March 1999 on the day after a night out at Batley’s Frontier club.
Police launched a murder investigation earlier this year and now want to speak to a “well spoken” woman, who lived temporarily with the 40-year-old in 1998, as did a man called Fraser.
The unnamed woman was aged in her mid 30s in the late 90s. At the time she was tall, slim, and had dark, wavy, shoulder-length hair.
“Fraser” was in his early 20s, 5ft 6ins to 5ft 7ins tall, thin, with dark brown hair.
He used to wear a full-length black leather coat or a blue RAF style overcoat and would sometimes go to the Frontier nightclub, and may have worked in the Manchester area.
Detective Chief Inspector Mark McManus, of West Yorkshire Police’s Homicide and Major Enquiry Team, said: “We are keen to identify this man and woman who we believe may be able to assist us in to our ongoing enquiries in to Bruce’s disappearance.
“We understand they both lived with Bruce temporarily at separate times during the year before he was reported missing.
“I would urge this man and woman, or anyone with further details about them, to please call the Homicide and Major Enquiry Team on 01924 334605 or via 101. Information can also be passed to independent crime-fighting charity Crimestoppers anonymously on 0800 555 111.”
Mr Gapper - described as a creature of habit who always went to the Frontier club on a Saturday night - was reported missing after he failed to turn up for work on the morning of Monday, 15 March, 1999.
The last confirmed sighting of him was at 1.30pm on the Sunday when a neighbour saw him unloading shopping from his car.
When police searched the home a half-eaten sandwich and nearly-full drink were found, suggesting that he left in a hurry.
He did not turn up for work on Monday morning, the day his red Peugeot 309 was found near the Castle Hill Monument in Huddersfield.
His bank card was used three times after he was last seen; firstly in Heckmondwike, then in Scarisbrick, near Southport, and finally in the Morley area four days after his disappearance.