HONG KONG (AFP) - Hong Kong police are seeking the Internet user behind a Facebook group that encouraged teenagers to commit mass suicide, a report said Thursday, after a 15-year-old member tried to kill himself.

Nearly 190 people joined the group "I have to practise suicide," which called on members to take their own lives on December 21, the daily South China Morning Post reported.

However the site's unknown creator had also posted a message on the social networking site saying that the group was just an "inside joke," the Post said.

Members were supposed to talk about ways to die in a "retarded way," such as "jumping off a chair," the creator wrote, adding: "I'm not encouraging suicide. It's supposed to be an inside joke."

The site was removed from Facebook when local media reported the story.

Police launched their investigation after classmates stopped a teenage boy who belonged to the group from throwing himself off the roof of their school two weeks ago in Tin Shui Wai.

The working class neighbourhood in the city of seven million has been nicknamed "City of Sadness" because of its social and domestic violence problems.

Last year, a mother and her two young children died in a grisly murder-suicide in their Tin Shui Wai home.