Shares of social media firms fell sharply on Friday as Twitter Inc joined the Snapchat owner in signaling a cutback in digital ad spend as economic growth sputters.

Pinterest Inc plunged 7.5%, Facebook-owner Meta Platforms Inc dropped 4.6%, Google-owner Alphabet Inc, which also sells ads online, fell 2.1%.

At current prices Pinterest, Meta, Alphabet and Snap were collectively set to lose about $36 billion in market value.

Twitter also blamed its ongoing battle to close its $44-billion acquisition by Elon Musk for the surprise fall in quarterly revenue. The micro-blogging site's shares were marginally higher.

Advertisers have pared back spending amid rising interest rates and surging inflation as some of them struggle with labor shortages and supply chain disruptions, Snap Inc said on Thursday.

"If you want proof that companies are nervous about the economic outlook, just look at how media platforms and marketing agencies are bemoaning a tougher advertising market," Russ Mould, AJ Bell investment director, said.

Investors are bracing for the slowest global revenue growth in the history of the social media sector as Apple Inc's privacy changes further cloud outlook.

Snap Inc's shares were down 34.6% and were the most heavily traded across U.S. exchanges, as the company said it was looking for new sources of revenue to grow.

The Snapchat owner's weak quarterly outlook confirm fears that ad spending is worsening, RBC Capital Markets said in a note.

"Unfortunately for Snap and the digital ad sector, we believe there are signs of further ad spending cuts."

Meta and Alphabet are slated to post quarterly results next week, while Pinterest is set to report second-quarter results on Aug. 1.