The outcome could influence thousands of similar cases against the tech companies brought by parents, attorneys general and ​school districts.

At least half of American teens use YouTube or Instagram daily, according to the Pew Research ​Centre.

The Los Angeles case involves a 20-year-old woman who said she became addicted to the apps ⁠at a young age because of their attention-grabbing design.

The plaintiffs in the Los Angeles proceeding focused on ​platform design rather than content, making it harder for the companies to avert liability.

Snap and TikTok were also defendants ​in the trial.

Both settled with the plaintiff before it began. Terms of the agreements were not disclosed.

Shares of Meta Platforms were up 1%, and Alphabet was slightly higher after the verdict, but little changed on the news.

A Meta spokesperson said, “We respectfully disagree with the verdict and ​are evaluating our legal options.”

Google did not have an immediate comment.

Mounting criticism

Large technology companies in the US have ​faced mounting criticism in the last decade over child and teen safety.

The debate has now shifted to courts and state ‌governments.

The ⁠US Congress has declined to pass comprehensive legislation regulating social media.

At least 20 states enacted laws last year on social media usage and children, according to the nonpartisan National Conference of State Legislatures, an organisation that tracks state laws.

The legislation includes bills that regulate the use of cellphones in schools and require users to verify their ages to ​open a social media account. ​

NetChoice, a trade association ⁠backed by tech companies such as Meta and Google, is seeking to invalidate age verification requirements in court.

A separate social media addiction case brought by several states and school districts ​against technology companies is expected to go to trial this summer in federal court ​in Oakland, California.

Another ⁠state trial is slated to begin in Los Angeles in July, said Matthew Bergman, one of the attorneys leading the cases for the plaintiffs.

It will involve Instagram, YouTube, TikTok and Snapchat.

Separately, a New Mexico jury on Tuesday found Meta violated ⁠state ​law in a lawsuit brought by the state’s attorney general, who accused ​the company of misleading users about the safety of Facebook, Instagram and WhatsApp and of enabling child sexual exploitation on those platforms.