(Reuters) -Pinterest ( PINS ) shares sank 18% on Wednesday as its dour forecast fueled fears the image-sharing platform is struggling to find new avenues of growth amid tariff pressures and competition from bigger rivals.

The share slump is set to erase $4.36 billion from the company's market value, if the premarket trading losses hold over the day.

Pinterest's ( PINS ) results are in contrast with upbeat third-quarter revenue posted by digital ad bellwethers, including Google-parent Alphabet, Meta and Reddit, which were driven by robust advertisement spending.

Platforms such as Meta's Instagram and Facebook, and TikTok have become the preferred choice for global retailers heading into the holiday season due to their sprawling user bases and integrated advanced AI tools.

CFO Julia Donnelly flagged softer ad spends in the United States and Canada, the company's most lucrative market, in the third quarter as "larger U.S. retailers navigate tariff-related margin pressure in the current environment."

Retailers, especially China-based firms such as Temu and Shein, have scaled back their marketing budgets following the removal of the "de minimis" exemption and tariff-driven uncertainty.

"Performance has been fine, but we struggle to see a catalyst to drive the business and accelerate growth," Piper Sandler strategists said.

Pinterest ( PINS ) expects quarterly revenue between $1.31 billion and $1.34 billion, with the midpoint below analysts' average estimate of $1.34 billion, according to LSEG-compiled data.

"In a market where companies' ability to deliver upward revisions from investments and innovation is important to driving multiple and share price appreciation, PINS failed to deliver," Morgan Stanley analysts added.

So far this year, Pinterest ( PINS ) has gained 13.6%, higher than Meta's 7.2% gain in the same period.