It is highly unusual for an app to top Apple’s chart so soon after its launch without a major marketing campaign.
However, the viral success of the product has raised concerns.
Previous anonymous online Q&A services have been blighted by abuse and bullying.
And one UK-based children’s charity has said that Snapchat itself might have to intervene.
“Apps such as Yolo that allow anonymous comments could be easily misused to send abusive or upsetting messages,” the National Society for the Prevention of Cruelty to Children (NSPCC)’s Andy Burrows told the BBC.
“Snapchat should justify how this app meets their duty of care to children.”
Does being anonymous make it easier to be mean?
A US-based child safety campaign group has also suggested that Yolo’s age rating is too low.
“Anonymity… has always created a breeding ground for hate and very poor teen decision-making,” said Protect Young Eyes.