The rape investigation was launched after the 21-year-old woman was attacked in Union Terrace Gardens in the early hours of 28 January.
Crimestoppers has offered the reward of up to £5,000 for information that leads to conviction in the case.
The charity stressed the reward would only be paid if information was passed to Crimestoppers directly.
Angela Parker, the Crimestoppers national manager for Scotland, said: "This attack was on a young woman in the heart of Aberdeen.
"We are now offering a substantial reward for anyone with information to contact Crimestoppers anonymously.
"By contacting Crimestoppers, via the phone (0800 555 111) or our anonymous online form, we don't ask for any personal details, you won't have to speak to the police, and you won't have to go to court. Just tell us what you know, not who you are."

Marc Martin, 22, and Matt Preece, 21, died after the BMW crashed in High Beeches Lane, Handcross, West Sussex, in December 2014.
Mr Martin, from Haywards Heath, and Mr Preece, of Lindfield, were both sitting in the back of the BMW.
Kyle Witney, 21, of Lindfield had previously admitted two counts of causing death by dangerous driving.
Witney has been jailed for six years at Lewes Crown Court.
The court heard Witney had been smoking cannabis and had gone out to get more drugs when the crash happened.
His girlfriend said at the time of the crash he had been showing off in front of his friends "trying to be smart".
The jury was told Witney had said immediately after the crash: "Oh my God, what have I done? I hope I haven't killed my friends."
He told paramedics he had been driving at 100mph.
Mr Martin and Mr Preece were taken to hospital after the crash but died from their injuries.
A 16-year-old girl who was a front-seat passenger in the BMW was also treated in hospital for minor injuries.
Witney had been left the BMW by his grandfather three months before the crash, the court was told.

The position became vacant after Angus Robertson lost his seat in the general election.
Ian Blackford, Joanna Cherry, Tommy Sheppard and Drew Hendry have all confirmed their candidacy. They were all first elected in 2015.
The party said its new Westminster group leader would be announced on Wednesday evening.
The SNP won the general election in Scotland, despite losing 21 seats. They will start the new parliament with 35 MPs.
Mr Robertson lost his Moray constituency seat to the Conservatives' Douglas Ross after Thursday's vote.

The General Penitentiary of Venezuela in central Guarico state was closed in October after violent clashes between inmates.
The bodies, which are in an advanced state of decomposition, were found during works to refurbish the jail.
So far none of the remains have been identified.
The grave was discovered on Thursday and the number of bodies found since has risen from seven to 14.
Forensic experts are continuing with their search and have not ruled out finding more bodies buried on the prison grounds.
On Friday, prison minister Iris Varela wrote on Twitter that she had contacted the relatives of two inmates to ask for their help identifying the remains.
The two prisoners disappeared when inmates were relocated from the General Penitentiary of Venezuela to other jails in October.
An estimated 9,000 prisoners were locked up in the jail near the town of San Juan de los Morros prior to its closure, according to non-governmental organisation A Window on Freedom.
The NGO says Venezuelan jails are woefully overcrowded and that last year 173 inmates died while in custody.
But Ms Varela told Venezuelan state broadcaster VTV that the country had taken huge steps to improve the conditions of its prisons.
She said that all of the country's women's and youth prisons had been brought up to new standards set by the Venezuelan government.
"This is an achievement without precedent of the Bolivarian Revolution and the government of our president, Nicolas Maduro," she said.
She said that President Maduro had asked her in 2014 to "impose maximum discipline" in Venezuelan jails.
"Well, here I am fulfilling the president's orders," she said.
She did not refer further to the remains found except to say that forensic tests were being carried out.
A £5,000 reward has been offered for information after a young woman was raped in Aberdeen earlier this year.
[NEXT_CONCEPT]
A man has been jailed after two of his friends died when his car hit a tree and flipped onto its roof.
[NEXT_CONCEPT]
Four SNP MPs have said they are hoping to be the party's next leader at Westminster.
[NEXT_CONCEPT]
The number of bodies found in a mass grave in Venezuela's largest prison has risen to 14, the public prosecutor's office said in a statement.