Feb 12 (Reuters) - Pinterest forecast first-quarter revenue below estimates on Thursday, underscoring the image-sharing platform's ongoing struggle to compete for advertising dollars against deep-pocketed platforms, sending its shares down 17.3% in extended trading.

Social media giants like TikTok and Meta's Instagram and Facebook continue to take a larger chunk of the market as their massive user bases and advanced artificial intelligence tools for ad creation keep luring advertisers.

The forecast comes on the heels of stronger results from rivals Snap and Reddit, both of which have reported upbeat holiday-quarter revenue.

But Pinterest aims to attract more marketers via its AI-powered Performance+ ad suite — having hired former advertising head of Spotify, Lee Brown — and longtime Amazon marketing executive Claudine Cheever, to stand out in a crowded ad market.

Last month, Pinterest had cut about 15% of its workforce, as it plans to reallocate resources to its AI-focused roles and strategy, which failed to spark enthusiasm from investors, who looked at the move as "more defensive than strategic."

For the first quarter, the company sees revenue in the range of $951 million to $971 million, below the analysts' average estimate of $980.1 million, according to data compiled by LSEG.

The company's ended 2025 with 619 million global monthly active users, up from the 553 million it had reported in 2024, a sign that Pinterest's core product remains appealing to consumers seeking inspiration for everything from home decor to fashion and recipes.

Revenue for the fourth quarter grew 14% to $1.32 billion, largely in line with estimates of $1.33 billion.