Willie Maughan (35) and Latvian national Anastasija (Anna) Varslavane (21) were last seen in Gormanston, Co Meath, on the afternoon of Sunday, April 14th, 2015.
Last year Mr Maughan’s father told The Irish Times the couple were murdered because gangland criminals feared they could implicate them in a gun murder.
Mr Maughan was associated with a gangland criminal based in north Co Dublin who is believed to be responsible for the murder of Benny Whitehouse.
Mr Whitehouse was shot on Clonard Street in Balbriggan, Co Dublin, on September 25th, 2014, shortly after dropping his six-year-old daughter to a nearby national school.
His wife was wounded in the same attack, which was believed to be linked to an ongoing feud in the area.
Abduction
Gardaí believe Mr Maughan knew Mr Whitehouse’s killers so they abducted and murdered him before concealing his body.
According to gardaí, both individuals were known to frequent the Balbriggan, Stamullen and Gormanston areas along the Dublin-Meath border.
Ms Varslavane is described as 1.67m, slim with long dark hair.
Mr Maughan is described as 1.72m, with an athletic build, a shaved head and green eyes.
Gardaí have carried out extensive searches in Co Meath and north Co Dublin with a view to finding their remains.
Anyone with information is urged to contact Ashbourne Garda station on 01-8010600 or the Garda Confidential Line at 1800-666111.