The investigation came as Italy announced it had temporarily blocked access to TikTok for users whose age could not be proved definitively.
According to TikTok's terms and conditions users must be at least 13-years-old.
The girl died in a Palermo hospital after being discovered on Wednesday by her five-year-old sister in the family bathroom with her cellphone, which was seized by police.
TikTok, which is owned by Chinese company ByteDance, said on Friday it had not managed to identify any content on its site that could have encouraged the girl to participate in any such challenge, but was helping the authorities in the probe over possible “incitement to suicide”.
“The safety of the TikTok community is our absolute priority, for this motive we do not allow any content that encourages, promotes or glorifies behaviour that could be dangerous,” a TikTok spokesman said.
The Italian Data Protection Authority said in a statement later on Friday that it would “block the (Chinese) social media network” with immediate effect until February 15, by which date the network will have to meet the regulator's demands.
Medical experts have warned about the danger of the challenge being taken up by some young people, who refer to it as “scarfing” or “the choking game” in which restricted oxygen to the brain results in a high.
The girls' parents told La Repubblica newspaper that another daughter explained that her sister “was playing the blackout game”.
“We didn't know anything,” the girl's father told the paper.
“We didn't know she was participating in this game. We knew that (our daughter) went on TikTok for dances, to look at videos. How could I imagine this atrocity?” he said.
Italy's data protection agency filed a lawsuit against TikTok in December, alleging a “lack of attention to the protection of minors” and criticising the ease with which very young children could sign up to the video app.
TikTok, which went global in 2018, has built its rapid success on its parodies, messages and short dance or comedy video performances set against popular music — along with an algorithm that determines which content is most likely to interest each user.
The death of the young girl provoked strong reactions in Italy and calls for better regulation of social networks.
“Social networks can't become a jungle where anything is allowed,” said Licia Ronzulli, president of Italy's parliamentary commission on child protection.