Paul Hunter Redpath, who was convicted of sexually assaulting two sisters in Downpatrick in 2005, was last seen in Aberdeen on 19 July 2011.
The 40-year-old from Stranraer was jailed for three years for the crime, but was released in 2006, because of time spent on remand.
Redpath went on the run within hours and was found in the Republic doing odd jobs for a Methodist minister.
At the time, police warned that Redpath was a danger to women and children, especially after drinking alcohol.
He was found and put on licence in 2007, which he then broke by drinking.
In 2009, the former chef was accepted to a south Belfast hostel and a judge imposed stricter restrictions on him, and ordered Redpath to sign the sex offenders register for life.
He fled for a second time and was found by GardaĆ in the Republic and advised to return to Northern Ireland days later.
Redpath was returned to prison where he remained until January 2010, when his sentence was completed.
It is now alleged that Redpath has failed to comply with registration requirements.
Grampian Police Chief Inspector Allan Ross said: "We have contacted our colleagues nationally along with partner agencies in relation to tracing Redpath, however there have been no recent sightings of him.
"We are issuing this appeal to the public to assist us in tracing him and I would urge anyone with any information about Redpath or of his current whereabouts to contact us."
