By Jaspreet SinghAug 4 (Reuters) - Image-sharing platform Pinterest 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 ‌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. Pinterest's ‌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.