Meta’s business can be boiled down to four words that begin with the letter H: hook, hold, harvest, hide, according to a lawyer who is prosecuting the world’s largest social media company.

The owner of Facebook and Instagram “hooks” in users, “holds” them on its platforms for as long as possible, “harvests” their data and then “hides” the truth from the public, she argued.

“Meta’s business model worked especially well for kids,” said Megan O’Neill, a lawyer for the state of California.

Her accusation opened the blockbuster trial against the US tech company on Tuesday in Oakland, California, just north of Meta’s headquarters in Silicon Valley. California has joined 28 other US states in suing the £1tn ($1.36tn) company for allegedly designing addictive products that lead to children being harmed.

View image in fullscreen Lennon Torres of Heat Initiative holds a banner with the names of young people who died as a result of social media outside the Ronald V Dellums federal building on 18 August. Photograph: Noah Berger/AP

Eight jurors heard from O’Neill and attorneys for Meta this week, along with testimony from former employees and a psychologist. The lawsuit centers on allegations that the company violated US federal child privacy laws and state-level consumer protection laws by collecting data on children under the age of 13 without parental permission. Over the course of the trial, the jury is additionally expected to hear from Meta CEO Mark Zuckerberg and Instagram CEO Adam Mosseri.

The threat to Meta is existential. If the company is found liable, damages could be as high as $200bn – an amount equivalent to the company’s 2025 annual revenue. The states are also asking that Meta be forced to change the design of its products to make them safer for children, which could have permanent effects on the company’s business model and how its social media platforms operate.

Meta has denied all allegations. Liza Crenshaw, a spokesperson for the company, said: “Rather than sticking to the facts or the law, the states have instead decided to chase an outlandish payout.”

During opening statements, Paul Schmidt, an attorney for Meta, said there is “no dispute” people can struggle with social media, but that Meta had “come up with tools to try and address that”. He added the company does not allow children under the age of 13 to register for accounts on its social networks and that it had disabled more than 1m accounts of those young users.

View image in fullscreen Paul Schmidt, lead attorney for Meta, leaves the courthouse as Meta is on trial over social media addiction in Oakland on 19 August. Photograph: Karl Mondon/AFP/Getty Images

The trial is expected to last six to eight weeks. The proceedings will be led by attorneys for the states of California, Colorado, Kentucky and New Jersey. The jury’s role is advisory, which means they will give recommendations to the presiding judge, Judge Yvonne Gonzalez Rogers, who will make the final decision on the verdict and damages.

Meta faces thousands of similar US lawsuits brought by families, school districts and other attorneys general. The company lost the first two of those cases to go to trial in March. In the first, the company was ordered to pay nearly $1bn to the state of New Mexico for allowing child sexual exploitation on its platforms; and in the second, it was found liable for deliberately designing addictive products that hooked one young woman and was ordered to pay her more than $4m.

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The star witness to take the stand in the trial’s first week was Arturo Béjar, a safety engineer at Meta who worked there in two separate stints between 2009 and 2021. Since leaving, Béjar has been an outspoken critic of the company, testifying before a US Senate committee and serving as an expert witness in other cases that involve social media’s harm to children.

In Oakland, Béjar testified that his motivation for pursuing solutions for harms to children was his own teenage daughter’s treatment on Instagram. He said she received unwanted sexual advances and photos of male genitals as well as misogynistic insults. Later, she told her father that reporting these abuses through Instagram’s established processes was either ineffective or not possible.

“Meta is taking a ‘don’t ask, don’t tell’ strategy” when it comes to child safety, Béjar testified.

View image in fullscreen Arturo Bejar, a former Meta safety engineer and consultant, leaves the courthouse as Meta faces trial over claims that they illegally collected and used children’s data. Photograph: Manuel Orbegozo/Reuters

Béjar said that his job often included briefing Zuckerberg and that he had spoken with the CEO more than 100 times in the course of his work.

During Béjar’s testimony, attorneys for the government showed the jury an email he sent Zuckerberg in 2021, which outlined a survey he had conducted of teens’ experiences on Instagram. The results showed 51% of users said “yes” to having bad or harmful experiences within the previous seven days and that content was taken down only 0.02% of the time.

Béjar testified he sent that data to Zuckerberg because, “in my experience, when Mark makes something a priority, mountains move.”

“Did he ever respond to you?” the attorney asked.

“No,” Béjar replied. “I didn’t hear back from him.”

Meta fought to bar Béjar from testifying at the trial, filing a series of motions to strike his exhibits and prevent him from taking the stand, all of which were rejected. In an email to reporters on Wednesday, Meta continued to hound him. The company’s statement said Béjar’s testimony was not credible or reliable because he overinflated his role at the company and took credit for work he didn’t do.

After Béjar’s testimony wrapped, the jury heard recorded depositions from Elena Davis and Natalie Troxel – both former user experience researchers for Meta. Jean Twenge, a psychology professor at San Diego State University, also briefly took the stand, with testimony scheduled to continue next week.