Fans of actor Song Joong-ki are forewarned of the existence, and rapid growth, of social media pages claiming to be managed by the actor personally, Song's talent agency said Monday.

An Instagram user posing as Song shared a photo of the actor in Greece along with the comment, "THANKS for support," earlier this day, but the account has been declared fake by the agency Blossom Entertainment.

"Song Joong-ki was briefly on Cyworld in the past, but he hasn't used any social networking services (SNS) since then," an agency official said. "There are currently no SNS accounts run by him or the agency."

Cyworld is a South Korean SNS website that was popular in the 1990s and 2000s.

"We try to report fake accounts because they may confuse people, but the criteria that make an account fake aren't clear-cut," the official said. "We've asked some users to stop (posing as the actor), but it's hard when they don't cooperate."

Song plays Capt. Yoo Si-jin in "Descendants of the Sun," which is broadcast in South Korea and China simultaneously.

The show has been a critical success, nearing 30-percent viewership nationwide in South Korea and garnering hundreds of millions of views on the Chinese streaming website iQiyi.

New episodes of "Descendants of the Sun" come out every Wednesday and Thursday at 10 p.m. in South Korea and China. (Yonhap)