The video, which was posted on YouTube just before 4pm on Tuesday, shows the 17-year-old girl being jeered and encouraged to perform sexual acts on a young man. It was removed within minutes.
However, a Twitter user repeatedly posted fresh links to the video throughout yesterday. The account also names the girl in question.
Facebook, Twitter, and Instagram have all removed pictures and videos involving the girl in recent days.
Gardaí said they expect to formally interview the teenager “in the next day or so”.
It is understood that the girl, believed to be from the West of Ireland, made a verbal complaint at the concert that she had been sexually assaulted at the venue. It is not believed to relate to the events shown in the pictures and videos which have been posted online.
“Our priority is the welfare of the girl involved and that of her family,” said a garda spokesperson. “There is an active investigation underway. We are monitoring CCTV and social media, as this is where this seems to have started. We would appeal to any witnesses to come forward if they have any information which might be of use.”
Following the concert, the girl was treated at a hospital in the midlands. Gardaí are also awaiting results of blood tests in an effort to establish if her drink was been spiked.
It is also investigating reports that a man from West Belfast is responsible for posting pictures of the girl performing a sex act at the concert.
In the video, the girl is seen kissing a young male in a maroon shirt while surrounded by a number of male and female teenagers or young adults.
In the two-minute recording, most of the group can be clearly heard jeering the teenage girl and encouraging her to perform oral sex on the male.
After turning to kiss another male, who does not engage with her, one female can be heard shouting to the male: “See what you missed out on?”
The female later asks: “Does anyone actually know her?” before a male responds: “Fuck no.”
As the girl continues to kiss the male in the maroon shirt, a number of watching males outline that he had performed a sexual act on the girl, while others encourage her to perform oral sex on the man.
Another male responds to a question as to why people are watching her, stating: “This is a show on its own, like. It’s fucked up.”
Another onlooker describes the incident as “sick altogether”. “In the middle of the day, 80,000 people around her,” he states.
The video ends with a shot of two males looking at their phone screens and smiling, perhaps indicating that they had either pictured or videoed the event.
When contacted by the Irish Examiner, Slane Castle owner Henry Mountcharles said he would not comment on the incident, as it would be inappropriate for him to do so.