The app, Sarahah, has swept into Ireland, overtaking Twitter and Tinder on the Irish app charts. It facilitates anonymous comments about those using the app.
However, teachers at one of Dublin's biggest secondary schools say it is being used by some children to bully others.
The city centre girls' school, which asked not to be named, has banned the Sarahah app and advised parents to delete it from their children's phones.
"Please check your daughter's phone for the Sarahah app," wrote a senior school administrator.
"This app is used to send anonymous messages, some of which may be nasty. Your daughters were asked to delete this app to ensure the well-being of all the students."
Experts have also warned that the app gathers all contact information from a user's phone and uploads it to its own servers.
The creator of the app, Saudi Arabian programmer Zain al-Abidin Tawfiq, said Sarahah harvests contacts from users for features "that will be implemented at a later time".
He said these user contact lists are being uploaded "for a planned 'find your friends' feature, which has been delayed due to a technical issue".
Launched in February, Sarahah now has 20 million users worldwide.
Its primary audience seems to be teenagers who screenshot compliments from other social media forums such as Instagram and Snapchat.
Sarahah presents itself as an app that "helps you self-develop by receiving constructive an- onymous feedback". Its creator says it is a way by which friends can point out personal strengths or weaknesses.
Earlier this year, a UK study into Irish teenagers found that cyberbullying was a significant factor in producing negative perceptions about body image.