The lawsuits filed separately in New York, California, the District of Columbia and 11 other states, on Tuesday expand Chinese-owned TikTok's legal fight with US regulators, and seek new financial penalties against the company.
The states accuse TikTok of using intentionally addictive software designed to keep children watching as long and often as possible and misrepresenting its content moderation effectiveness.
"TikTok cultivates social media addiction to boost corporate profits," California Attorney General Rob Bonta said in a statement.
"TikTok intentionally targets children because they know kids do not yet have the defences or capacity to create healthy boundaries around addictive content."
TikTok seeks to maximise the amount of time users spend on the app in order to target them with ads, the states say.
"Young people are struggling with their mental health because of addictive social media platforms like TikTok," New York Attorney General Letitia James said.
TikTok insists that it offers robust safeguards for its young users. (AP PHOTO)
TikTok said last week it strongly disagrees with allegations it fails to protect children, saying "in fact, we offer robust safeguards for teens and parents."
Washington DC Attorney General Brian Schwalb alleged TikTok operates an unlicensed money transmission business through its live streaming and virtual currency features.
"TikTok's platform is dangerous by design. It's an intentionally addictive product that is designed to get young people addicted to their screens," Schwalb said in an interview.
Washington's lawsuit accused TikTok of facilitating sexual exploitation of underage users, saying TikTok's live streaming and virtual currency "operate like a virtual strip club with no age restrictions".
Illinois, Kentucky, Louisiana, Massachusetts, Mississippi, New Jersey, North Carolina, Oregon, South Carolina, Vermont and Washington state also sued on Tuesday.
In March 2022, eight states including California and Massachusetts, said they launched a nationwide probe of TikTok impacts on young people.
The US Justice Department sued TikTok in August for allegedly failing to protect children's privacy on the app.
Other states previously sued TikTok for failing to protect children from harm, including Utah and Texas.
TikTok on Monday rejected the allegations in a court filing.
TikTok's Chinese parent company ByteDance is battling a US law that could ban the app in the United States.
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