Zuckerberg, 41, leads Meta, the parent company of Facebook, Instagram and WhatsApp. He is expected to be the most closely watched witness in the California case, the first in a wave of lawsuits that could shape legal standards for thousands of similar claims filed by American families against leading tech companies, News.Az reports, citing AFP.
The trial marks the first time Zuckerberg will address the safety of his platforms directly before a jury.
His presence has loomed over the proceedings since jury selection, when Meta’s legal team sought to exclude potential jurors in California whom they considered overly hostile toward the Facebook founder.
Twelve jurors in Los Angeles will hear testimony through late March as they consider whether Google-owned YouTube and Meta’s Instagram share responsibility for mental health issues experienced by Kaley G.M., a 20-year-old California resident who has used social media heavily since childhood.
Kaley began using YouTube at age six, joined Instagram at 11, and later used TikTok and Snapchat. The case seeks to determine whether Google and Meta deliberately engineered their platforms to encourage compulsive use among young people, potentially harming their mental health.
Along with two related trials scheduled for this summer in Los Angeles, the proceedings are expected to influence the handling of thousands of lawsuits that accuse social media companies of contributing to rising rates of depression, anxiety, eating disorders and suicide among youth.
The case focuses specifically on platform design, algorithms and personalization tools. Under U.S. law, social media companies are largely shielded from liability for user-generated content, so the legal arguments center on product design rather than posted material.
TikTok and Snapchat, also named in the complaint, reached confidential settlements with the plaintiff before the trial began.
Instagram chief Adam Mosseri testified earlier this month, telling jurors he prefers the term “problematic use” over “addiction.” He compared excessive social media use to binge-watching a television series, arguing that it does not equate to clinical addiction.
In the courtroom gallery, several mothers whose teenage children died by suicide attended the proceedings. Some had camped overnight outside the courthouse to secure seats.
Plaintiff attorneys also called psychiatrist Anna Lembke, who testified that social media can function as a “gateway drug” for young users, potentially reshaping developing brains toward addictive behaviors.
During testimony, Mosseri defended a 2020 decision approved by Zuckerberg to allow cosmetic surgery filters on Instagram, despite internal objections warning of potential harm to young girls. Some executives reportedly supported reinstating the filters to remain competitive with TikTok.
Although YouTube CEO Neal Mohan had been expected to testify, plaintiff lawyers said Tuesday they would instead call another YouTube executive.
The Los Angeles trial is unfolding alongside a nationwide case before a federal judge in Oakland, California, which could lead to another trial in 2026.
Separately, Meta is facing trial in New Mexico, where prosecutors allege the company prioritized profits over safeguarding minors from sexual exploitation.
