Shares of Pinterest Inc fell about 20% before the opening bell on Friday and were set to start trading at more than a three-month low, after the company warned of slowing user growth in the United States, its largest market.

At least eight brokerages cut their price target on the stock, which fell to $57.60 in pre-market trading. If the losses hold, about $9 billion would be swiped off its market capitalization which currently stands at about $36.8 billion.

J.P.Morgan made the most aggressive cut and slashed its target by $27 to $68, pushing it well below the current median price target of $77, citing lower-than-expected user additions in the latest reported quarter and disappointing third-quarter outlook.

The brokerage also cut its rating on the stock to "neutral" from "overweight".

Overall monthly active users (MAUs), a widely watched metric, rose by only 9% and missed analysts' expectations in the second quarter. It had risen 30% in the prior quarter.

The company also said that user growth in the United States was decelerating as people who used the platform for crafts and DIY projects during the height of the pandemic step out more as curbs ease.

"This performance suggests lockdown benefits were more transitory than anticipated, while an apparent growing pivot towards the 'creator economy' does raise concern regarding structural engagement trends," James Cordwell, analyst at Atlantic Equities said in a post-earnings note.

Of 30 analysts covering Pinterest, 19 rate the stock "buy" or higher, 10 "hold" and one recommends "sell".

Pinterest shares, which were the biggest losers among NYSE-listed stocks pre-market, have fallen about 9% so far this year compared with a 18% rise in the broader S&P 500 index.