Allan, who was 23 when he went missing, was last pictured on CCTV in Caskieberran Road, Glenrothes, shortly after 2am on Sunday, 3 November, 2013.
The previous night (Saturday, 2 November, 2013) Allan had walked with friends to an engagement party at Leslie Golf Club from his home in Ednam Drive.
He arrived at the golf club around 9pm and left about midnight when he travelled by minibus to Styx nightclub.
Allan and the group arrived at Styx shortly after and he left the club, which is approximately a one mile walk away from his home, at 2.02am.
Despite extensive searches and public appeals by Allan’s family and police, he has not been seen or heard from since.
Detective Chief Inspector Kevin Houliston of the Major Investigation Team said: "We remain committed to trying to get answers for Allan's family and any new details that we receive will be fully investigated.
"I would urge anyone who may hold information which could assist us, no matter how small it might seem, to report this as soon as possible."
Allan is described as white, 5ft 6ins tall, medium build, with short brown hair, blue eyes and tattoos on both arms.
When last seen, he was wearing a Voi t-shirt with three bands of colour – navy on the top, grey in the middle and white on the bottom, dark-coloured denim jeans and grey leather plimsolls.
Those who may be able to help can call Police Scotland on 101 or email OperationToner@scotland.pnn.police.uk
You can also contact the independent charity Crimestoppers anonymously on 0800 555 111, or call or text the charity Missing People on 116 000.