The attack took place in a Midlands town in December after she was offered a lift home.
Detectives arrested the five suspects on Wednesday.
All five males, who are aged between 17 and 20, were released without charge yesterday and a file on the case will now be prepared for the Director of Public Prosecutions (DPP).
The victim has been described as "extremely distraught and vulnerable" since the attack and is understood to come from a "loving and respectable family", sources said.
It is believed the girl got into a car in the town centre that was occupied by a man known to her.
She is not believed to have been forced into the vehicle.
It is alleged the girl was taken to another location and attacked by the men there.
The majority of the suspected attacks took place in this location. After the gang rape, it is understood that the girl sought help and gardaí were then notified of the incident.
A major investigation involving officers based in the Midlands then took place and CCTV footage was gathered and studied.
Forensic and other evidence was obtained by gardaí.
It is understood that when all this evidence was gathered, senior officers decided to make the arrests this week.
The suspects - one 17-year-old, two 20-year-olds and two 19-year-olds - were all picked up by gardaí on Wednesday and questioned at different stations in the Midlands before being released without charge yesterday evening.
They all live in the Midlands area and were not previously known for this type of offence.
The Central Statistics Office (CSO) said last year gardaí recorded 2,442 sex offences - a rise of 13pc in the 12 months from June 2015 to June 2016.
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