Twitter beat official Wall Street expectations with its first post-IPO quarterly earnings report, but many of the company's investors are selling anyway. The mixed-bag report contained some good news, but also included some stats that have driven away investors.

Scared by a lack of engagement and lower growth numbers than hoped for, Twitter's shares have been hit by a couple of major dips in the last two days, and may be on a downward trend for the foreseeable future. The stock, which peaked at over $74 in December is now down to $50 after Thursday trading brought down the price from Wednesday's close of $65.97.

Twitter's first report contained some superficially bad numbers, and some superficially good ones as well, creating a complicated picture for the newly public social media company.

The (not so) Bad

First, Twitter reported a fourth quarter net loss of $511.47 million, which might have scared away some investors. However, according to SFGate, that big red number include about $406 million in stock payouts to employees and early investors tied to the company's initial public offering.

Twitter's Q4 revenue was up 116 percent over last year, at $243 million and its ad revenue, meanwhile, was up 121 percent over last year, totaling about $220 million.

And Twitter has recently focused on attracting even more advertising, playing up its unique strong suit of diversity, starting with its Latino audience. These numbers beat expectations, but other signs of slowing growth have hurt Twitter's outlook.

The (not so) Good

Twitter ended 2013 with 241 million monthly active users, which is up 30 percent from the previous year.

But in that figure are signs of slowing growth which played against Twitter on Wall Street. In the last quarter of 2013, for example, Twitter only added 9 million monthly new users, and only 1 million were U.S.-based new tweeters. Compare that to early 2013, when the microblogging service was adding about 16 million new users each quarter, and you start to see the problem.

Another important user trend is down as well: engagement. This is the measure of how often users interact with social media services, and for Twitter, the numbers are not good. The number of times users looked at Twitter feeds, visited the website, or searched for something fell 7 percent in Q4 2013 from the previous quarter, according to the Washington Post.

Twitter's User Interface

One consistent criticism of Twitter's potential as a growing, public company has been its user interface (UI). The UI is the way users interact with a website or app.

Twitter's UI has always been somewhat inscrutable to new users. While Facebook has basic "posting" and "commenting" actions that can be easily understood by everyone including Grandma (something that may actually be detrimental to Facebook's popularity with younger teens), the assortment of actions on Twitter can bewilder those who have never tried it before or the technically un-inclined.

It's not that Twitter is difficult to use once you've gotten used to it, but amalgamation of tweeting, retweeting, direct messaging, favoriting, following, and hashtags can be intimidating to new users, not to mention making and sharing lists and the very core of Twitter -- the 140 character limit, which does take some getting used to.

Twitter CEO Dick Costolo admitted as much in his earnings conference call, telling investors he knows the UI is a problem and that the company is actively working to fix it. "There's a lot we can do to significantly improve the user experience," Costolo said, according to CNET. "We believe the changes we're making will lead to a much more satisfying user experience."

Costolo said Twitter didn't need to change the social media platform's fundamentals though, just make it simpler for new users to get the hang of the service. "We don't think we need to change anything about the core characteristics of our platform," he said. "We just need to make Twitter a better Twitter."