Parents warned to keep a check on teen using app Sarahah.

The Canadian Centre for Child Protection in Winnipeg is warning parents of the dangers of an app popular with teens called Sarahah.

The app allows users to send anonymous "constructive criticism" to friends and co-workers, but critics say it has turned into a platform for cyberbullying and harassment.

The centre is encouraging parents to talk to their teens about the harm it can cause and limiting their use of the app.

It is also advised that teens using  the app should remove themselves from the search function and only share their usernames with people they know.

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