Twitter (NYSE:TWTR) shareholders suffered in 2015. Shares of the social network closed the year down nearly 40%, trading near an all-time low. There was no shortage of unfortunate events that befell the company in 2015, but some stand out more than others.

Poor earnings reports take a toll
Three of Twitter's four earnings reports in 2015 were met with heavy selling. First in April, then again in July, and finally in October, Twitter shares plunged after the company turned in figures that disappointed both analysts and investors.

On April 28, Twitter shares fell 18% after the company's first-quarter earnings report was posted early (ironically leaked on Twitter itself). Twitter's revenue rose 74% on an annual base, reaching $436 million in the quarter, but that was worse than its own guidance and what analysts had been anticipating. To its credit, its monthly active user base (302 million) was in line with estimates, and it earned slightly more than anticipated. Crucially, however, Twitter's second-quarter revenue projection -- $470 million to $485 million -- was well below estimates.

On July 28, Twitter shares crashed again, falling 12% after the company's second-quarter earnings report. Twitter's revenue rose 64% on an annual basis to $502 million (better than its guidance), and it once again beat analyst expectations for earnings. But its monthly active user base rose only 8 million (to 316 million), and during the company's earnings call, CFO Anthony Noto told investors not to expect Twitter's audience to expand much more for a considerable amount of time.

In October, Twitter stock crashed one more time, falling another 12% after it posted third-quarter earnings. Twitter's earnings and revenue were better than anticipated, but its guidance fell short. In the fourth quarter, Twitter expected to generate $695 million to $710 million of revenue, far below the $742 million analysts had been expecting.

Sacca trashes Twitter's strategy
Those three earnings reports drove most of the decline in Twitter's stock price in 2015, but there were also negative headlines surrounding the company's management and direction. In a blog post on June 3, venture capitalist and Twitter investor Chris Sacca criticized the company's strategy, laying out a case for what Twitter could do. "Twitter has failed to meet its own stated user growth expectations," he wrote. "Twitter's efforts to convince the investing community of the opportunity ahead fell flat."

Just days later, on June 11, Twitter announced that its CEO, Dick Costolo, would be stepping down. That news was initially met with buying, as Twitter shareholders anticipated positive changes, but the need for the transition underscored Twitter's troubled status.

On Oct. 5, Twitter co-founder Jack Dorsey was named CEO after having filled that role on an interim basis after Costolo left. Twitter shares rallied somewhat in the wake of the announcement, but that was tempered by the fact that Dorsey would continue to serve as the CEO of Square, another firm he helped found. Back on June 22, Twitter's board had released a memo pledging that they would only consider candidates who could give a "full-time commitment" to the company, so Dorsey's appointment was something of a surprise.

Dorsey insisted that he could run both companies well, building teams that would "move fast, and learn faster." In time, Dorsey may be able to turn Twitter around, but in the meantime, shares have continued to trend lower.

Sam Mattera has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Twitter. 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.