Facebook's latest expectation-beating quarter is "as good as it can get" for the company, according to one analyst, who predicts shares could fall 30 percent in the next six months with the market at the "height of insanity" with social media stocks.

The social networking giant beat analyst forecasts on earnings per share in the third quarter late Wednesday with advertising revenues rising 59 percent year-on-year. Monthly active users grew 16 percent to 1.79 billion, while for the first time, more than 1 billion users were active only on their phones every month.

But Facebook shares fell over 7 percent after hours and were down nearly 6 percent in pre-market trade after Chief Financial Officer David Wehner said ad revenue growth could slow "meaningfully" in 2017.

Trip Chowdhry, managing director of equity research at Global Equities Research, said this is the top for the company.

"If you think about this quarter, it's as good as it can get because two major events happened in a single quarter. You have U.S. elections and the Olympics. This is not going to repeat for the next four years," Chowdhry told CNBC.

"They also had a tailwind because Yahoo was acquired by Verizon and the advertisers on Yahoo are moving away."