2015 was a fantastic year for Facebook (NASDAQ:FB) investors. Shares of the social networking giant surged, rising more than 36%, and closed the year trading near an all-time high. Facebook posted a steady stream of strong earnings reports, and rolled out a number of innovative new features. Not everything went well for Facebook, however. While it's hard to point out too many specific stories that weighed on shareholders in 2015, there were a few disappointments in the second half of the year.

Stumbling after earnings
Facebook shares fell in April and again in July after the company turned in its fiscal first- and second-quarter earnings reports. Facebook enjoyed strong sales and user growth in both quarters, but expenses seemed to worry shareholders.

Facebook earned $0.42 on $3.54 billion in sales during the first quarter, and $0.50 on $4.04 billion of sales in the second quarter. Those figures were roughly in line with analyst estimates, and in both periods, revenue rose around 40% on an annual basis. User growth was strong. Facebook ended the first quarter with 936 million daily active users, a 17% increase from the prior year. In the second quarter, that figure rose to over 1 billion, a 17% gain from the same quarter last year.

Yet those figures may not have been enough to meet investors' expectations, and steadily increasing costs weighed on Facebook's results. In the first quarter, Facebook's operating expenses jumped 83% on an annual basis, and they rose 57% in the second quarter.

Facebook shares fell in after-hours trading on April 22, the day it reported its first-quarter results. On July 30, the day following Facebook's second-quarter report, shares were down as much as 3%. Both instances ultimately proved to be buying opportunities, but at the time, there was concern about Facebook's results.

The European Union sides with a student
On Oct. 6, the European Union's highest court ruled in favor a student -- Max Schrems -- who had challenged Facebook's use of intercontinental data transfers. Previously, Facebook had operated under a 15-year-old pact that allowed it to easily transfer data between the U.S. and its European operations. Following the unprecedented leaks by Edward Snowden, including the disclosure of the NSA's Prism program, Schrems argued that Facebook was unfairly flouting European privacy laws and inadequately protecting the data of its tens of millions of European users. Facebook wasn't the only firm affected by the ruling, but it was a blow for the company. But not a significant one, especially not in the near term, and Facebook's stock didn't see much of a reaction. But it could make it more difficult for the company to operate in Europe going forward, and additional privacy legislation and penalties for noncompliance could put pressure on the company's results.

Marc Andreessen cashes out
In November, an SEC filing showed that famed venture capitalist Marc Andreessen had unloaded about three-quarters of his Facebook stock -- around 1.5 million shares, worth nearly $160 million -- in October and November. Andreessen remains a Facebook board member, and still owns several hundred thousand shares of the company, but any sales from such a famed tech investor are likely to be met with selling pressure. Facebook shares were down as much as 3% following the report.

In 2012, Facebook shares suffered a similar fate when Peter Thiel -- another venture capitalist and board member -- sold most of his stake following Facebook's lockup period. Facebook shares eventually recovered and then soared to new highs, making Thiel's sale look questionable in hindsight. Still, given Andreessen's status as an insider, the move lower wasn't unexpected.

Sam Mattera has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Facebook. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.