Aug 4 (Reuters) - Image-sharing platform Pinterest ( PINS ) forecast slower revenue growth for the third quarter on Tuesday, a sign of tough competition for digital advertising from bigger players including Meta's Instagram, sending its shares down 9% in extended trading.

Pinterest ( PINS ) has been expanding Performance+, its AI-powered suite for advertisers, to attract more marketers by helping them optimize and scale their campaigns with less manual effort.

As Meta continues to improve its Advantage+ ad automation tools, Reddit ( RDDT ) launched a broadly similar product and with ads becoming a larger focus for OpenAI, competition is expected to increase further.

Last month, Google revamped Google Images with AI-powered personalized feeds and visual discovery features resembling Pinterest ( PINS ), indicating a broader push for AI-driven search and shopping by the search-engine giant.

"We faced incremental pressure mid-quarter from Asia-based cross-border retailers impacted by regulatory actions particularly in Europe and that pressure is continuing in the third quarter," CFO Julia Donnelly said on the company's post-earnings call.

Pinterest ( PINS ) expects its current-quarter revenue to be in the range of $1.19 billion to $1.21 billion, representing a 13% to 15% growth, compared with analysts' average estimate of $1.20 billion, according to data compiled by LSEG.

That is slower than the 18% revenue growth in its second quarter. The company reported $1.18 billion in revenue for the three months ended June 30, beating estimates of $1.15 billion.

"Its AI tools have shown early promise, but they haven't generated the same level of enthusiasm as competitors' offerings," said Emarketer analyst Marisa Jones.

Pinterest's ( PINS ) global monthly active users rose 11% to 640 million in the second quarter from a year ago, while average revenue per user rose 7% to $1.86.

Earlier this year, the company completed its acquisition of tvScientific, a move aimed at extending advertisers' reach beyond social media and into connected TV and giving Pinterest ( PINS ) a broader pool of ad budgets.