The young girl treated in hospital after an injury sustained while "ghosting" hurt her back, torso and ankle.
Gardai said the youth was injured earlier this month near Limerick city while participating in the highly dangerous trend.
A garda spokesperson said: "Gardaí attended an incident in the southern region in recent days where a youth received a number of minor injuries while participating in this activity.
"Emergency services escorted the youth to hospital where she is being treated for injuries sustained to her back, torso and ankle.
"She was admitted to hospital for a number of days."
Gardai are warning about the new social media trend and and pleading with people not to take part.
A garda spokesperson added: "An Garda Síochána have been made aware of a social media trend circulating online called ‘ghosting’.
"This ongoing trend challenges persons to lie on a roadway with a sheet placed over them in an attempt to stop oncoming traffic. This activity is extremely irresponsible and poses a serious danger to those taking part in the ‘ghosting’ and motorists.
"An Garda Síochána are urging people not to engage in this social media trend. Gardaí are particularly appealing to parents to educate their children on the dangers of participating in such activity and to highlight the importance of being seen while using Irish roads."
