(REUTERS/Kacper Pempel)

"We suck at dealing with abuse and trolls," Twitter chief executive Dick Costolo admitted in a memo heard 'round the social network. In his note to the staff, leaked to The Verge late Wednesday, Costolo took personal responsibility for the company's shortcomings -- a problem that he said is costing Twitter "core user after core user."

Twitter bucked some doubts about its growth, reporting Thursday that the company has 20 percent more monthly active users than it did last February. But its quarterly growth has continued to slow. Revenue nearly doubled from the previous year to $479 million. Twitter also reported earnings of 12 cents per share, doubling analyst expectations.

Twitter’s shares increased 9 percent to nearly $45 in after-hours trading.

Twitter's growth has been slower than many  investors would like, which has prompted some investors to call for Costolo's ouster. Twitter's board, however, has been vocal about its support for the chief executive. Over the past several months, the company has rolled out several features  -- and reportedly struck a new deal with Google to include tweets in search results -- to broaden its appeal beyond its faithful, constantly plugged-in user base.

The company also has taken its first steps to reverse the perception that the Twitter community is lawless, caustic and abusive. That's come after several years of campaigning from women and minority advocates, capped off by high-profile incidents of abuse against women such as Anita Sarkeesian and Zelda Williams.

Though it wasn't as striking as what Costolo said in his e-mail to employees, Twitter admitted its shortcomings in a blog post in December. The company announced a new reporting tool aimed at making it easier to report abuse and forecast future plans to keep working on abuse.

We are nowhere near being done making changes in this area. In the coming months, you can expect to see additional user controls, further improvements to reporting and new enforcement procedures for abusive accounts. We’ll continue to work hard on these changes in order to improve the experience of people who encounter abuse on Twitter.

Costolo's comments could be seen as a reference to those future plans. A Twitter spokesman said that the company is continuing with its original plans to develop tools to give users more control over their own accounts in order to deal with abuse.

Still, Costolo's comments could be seen as evidence that there's a cultural shift happening at the company. Twitter has always been the social network that has taken the hardest line among social networks when it comes to protecting free speech, which has often put it at odds with anti-harassment activists.  Twitter has been loath to ban users outright, for example, but has started giving users more control to mute activity they don't want to see on the site.

But Twitter has been appearing to take on the issue more seriously at an institutional level, said Soraya Chemaly, a Washington-based activist who has lobbied Twitter for years to change its policies to be more receptive to the feedback women and minority users have given to the company.

In the past, Chemaly said that while individual employees at Twitter have been enthusiastic about helping her causes, it never seemed to very far beyond those personal connections. "I would categorize that as almost a 1-to-1 relationship," Chemaly said, of Twitter. But, she said, "in the past two months, there's been a lot more interest on behalf of the people that we talk to."

Chemaly said she's encouraged to hear information, even leaked information, that these concerns go straight to the top. But now the rubber must hit the road, she said. "There needs to be a point at which a company puts a stake in the ground and says, 'We do not accept this on our platform.'"

One thing that needs to change in these conversations, Chemaly said, is the notion that anti-abuse measures must be at odds with free speech. In her opinion, allowing abusive comments to stand also limits free speech -- and often the speech of women, minorities, or people with already unpopular opinions.

"The issue has always been framed as one of one person's safety versus another person's free speech," she said. "That's true for some people. But for others, safety and free speech are on the same side of the problem."