The $108 billion Fidelity Contrafund continues to have a big appetite for Facebook Inc's stock, adding to its position in the social media company during the third quarter and praising its mobile ad revenue growth and "visionary management."

The fund, which is the largest mutual fund owner of Facebook, disclosed adding to its position in its third-quarter commentary letter to investors on Monday.

"We continued to favor the stock, in large part due to its mobile-advertising business and visionary management team, and we added to the fund's stake during the quarter," according to the commentary letter.

The fund didn't say how much Facebook stock it bought, but ended August with about 42 million shares. That's up from about 36 million shares at the end of 2013.

Facebook accounts for about 2.8 percent of the assets in Contrafund, which is run by portfolio manager Will Danoff.

Facebook helped the fund beat the S&P 500 Index in the third quarter. The stock is up nearly 41 percent so far this year.

In the third quarter, Contrafund's retail shares returned 1.77 percent versus the benchmark's 1.13 percent advance.