Google's YouTube has settled a social media addiction case brought by a 15-year-old in Florida, in a fresh legal blow for online platforms accused of fuelling a mental health crisis among children.

The teenager, who used the initials R.K.C. in court documents, alleged that YouTube and other social media firms had designed their platforms to be addictive.

"This matter has been amicably resolved, and our focus remains on building age-appropriate products and parental controls that deliver on that promise," Google spokesman José Castañeda said in a statement to the BBC.

R.K.C. is also suing Instagram-parent Meta, TikTok, and Snap Inc in a trial currently set to begin on 27 July in Los Angeles.

R.K.C.'s allegations will be the second trial in a series being overseen by Los Angeles Superior Court Judge Carolyn Kuhl in order to resolve more than 1,000 similar cases in California.

The first trial occurred earlier this year, in which a 20-year old California woman, known as K.G.M., accused Meta and YouTube of intentionally designing platforms to be addictive to young users.

She had also sued Snap and TikTok, but both platforms settled before trial for an undisclosed sum.

A jury ultimately awarded K.G.M $6m (£4.5m), the first time a court had found that Meta and YouTube were liable for their platforms' mental health effects on certain users.

The same week, a jury in New Mexico told Meta to pay $375m for misleading users over the safety of its platforms for children.

R.K.C.'s claims are similar to those of K.G.M, according to court documents.

He claims that features like infinite scroll and autoplay, both of which continuously and automatically show users new content on a platform, drove compulsive use that became a type of addiction. It caused him anxiety and sleep deprivation, among other issues.

"As jurors saw in the first bellwether trial, leadership at these social media companies have been strategizing for years to hook children early and maximize their usage," said R.K.C.'s attorneys John Morgan and Emily Jeffcott in a statement.

Google told the BBC it had built YouTube "responsibly - working with families to give young people safer, more helpful experiences online" for more than a decade. The platform in 2015 launched YouTube Kids, a version designed and curated for children.

The company also last month settled another case that was heading to trial, in which a Kentucky school district accused YouTube, Meta, Snap and TikTok of creating a mental health crisis for its students.

All of the companies ultimately decided to settle instead of going to trial.

The school district wanted the companies to change their purportedly addictive features, but also to pay for the costs schools incurred in helping children deal with things like anxiety, depression and even self-harm allegedly driven by their social media use.

The trial was due to begin in mid-June in federal court in Oakland, California, as part of a multi-district litigation (MDL) that includes thousands of similar cases and claims.

Another trial in the MDL brought by US states against Meta is set to proceed in the same court starting in August.