Millionaire Lyons (51) has not been seen around his plush Griffith Avenue neighbourhood since leaving Wheatfield Prison under cover of darkness on December 14.
"The girl he attacked spent Christmas with her family. They looked after her and supported her, and we hear that Lyons was not discussed over the holiday period," said a neighbour of the sex attacker.
"He hasn't been seen around here, and nobody seems to know where he is, or if he's in the country at all," the neighbour added.
The wealthy businessman was sentenced to six years last July for sexually assaulting his victim in October 2010.
He rugby-tackled the young lady to the ground before sexually assaulting her.
Lyons admitted the attack but claimed he was overcome with an "irresistible urge" due to the combination of alcohol, the cholesterol medicine Rosuvastatin and cough syrup. The jury rejected his claim.
Dublin Circuit Criminal Court judge Desmond Hogan sentenced Lyons to six years in prison as well as ordering him to pay his victim €75,000 in compensation.
Judge Hogan said Lyons "had rugby-tackled this young lady to the ground in a dark area under trees on a quiet road".
"The long abiding psychological trauma suffered by her is perhaps seriously greater than the physical injuries she sustained," the judge commented.
However, after considering a psychiatric report, a probation report and testimonials, Judge Hogan said Lyons had up to then been "of good character" and was "unlikely to reoffend".
He then suspended five-and-a-half years of the sentence.
Lyons served four-and-a-half months behind bars with remission for good behaviour.
The Director of Public Prosecutions (DPP) subsequently applied to the Court of Criminal Appeal over what she believes was an "unduly lenient" sentence.
However, Lyons walked free from jail and was driven away in a BMW after that appeal was delayed.
The DPP tried last month to have the appeal prioritised so it could be heard before Lyons was released, but the court refused because counsel for Lyons was unavailable.
Another attempt to fix a date for the case will be made on March 11.
Neighbours of the young victim said she was "devastated" that Lyons is now out of prison and "allowed sneak out in the dead of night".
Hours after his release Lyons flew to London to watch his favourite football team, Queens Park Rangers, beating Fulham 2-1 at their Loftus Road ground.