Check out which companies are making headlines after the bell on Wednesday:

Twitter shares fell more than 3 percent after the company announced COO Adam Bain decided to step down and explore opportunities outside the company. Anthony Noto, who's served as the company's CFO since July 2014, has been named COO. Noto will continue to manage the live content business, and assume responsibility for Twitter's revenue-generating organizations, effective immediately. Bain will assist with the transition of the COO role over the coming weeks.

Taser International shares were up more than 6 percent after the bell, following its quarterly earnings report. The company posted earnings of 7 cents a share, beating analysts' estimates by a penny. The body camera-maker posted record revenues of $71.9 million, easily surpassing estimates of $59 million. The company also announced a transition plan for its CFO, Dan Behrendt, who will be leaving the company to pursue other opportunities. The company said Behrendt will remain in his current capacity through the filing of Taser's 10-K form, as the company commences a national search for a new CFO.

Shake Shack shares jumped as much as 11 percent after the closing bell on Wednesday after the company posted third-quarter earnings that beat expectations. Propelling the stock up was the company's higher-than-expected same-store-sales growth of 2.9 percent in the third quarter. Rival restaurants like McDonald's and Starbucks have posted weaker-than-expected same-store-sales growth in recent quarters, blaming election jitters, grocery prices and meal kit delivery services for why consumers were eating at home more often.

Shares of Mylan fell slightly after choppy trade Wednesday after the company reported earnings. The EpiPen maker missed analysts' expectations on both its top and bottom lines, posting adjusted earnings of $1.38 per share on revenues of $3.06 billion. Analysts expected earnings of $1.45 per share on $3.12 billion, according to a Thomson Reuters consensus estimate. It reported a GAAP loss of 23 cents a share, primarily due to a $465 million settlement with the U.S. Department of Justice over the classification of its EpiPen under the Medicaid Drug Rebate program.



Alexion Pharmaceuticals shares were down more than 2 percent after the company announced it would be delaying its quarterly filing due to an internal investigation. The company said the audit and finance committee of the board of directors is conducting an investigation into allegations that recently have been made by a former employee with respect to the company's sales practices of Soliris, a medication used to treat a certain blood disorder.

—CNBC's Sarah Whitten contributed to this report.

