Take a look at some of Thursday's midday movers:
Aegerion Pharmaceuticals - The biotechnology company fell after ts CEO bought 30,000.
Allergan - The drug manufacturer fell on news Valeant Pharmaceuticals International and activist investor Bill Ackman planned to push for changes on Allergan's board.
AMC Networks - The cable operator fell after ISI downgraded the stock to neutral from buy.
Cheetah Mobile - The Chinese security software maker rose in its market debut after offering 12 million ADR shares at $14 a share.
Chelsea Therapeutics - The central nervous system disorder specialist rallied after Denmark's H. Lundbeck said it would make a bid to buy the company.
Dean Foods - The dairy company declined after cutting its full-year profit outlook on rising milk costs.
DirecTV - Shares fell after Buckingham downgraded the stock to neutral from buy.
Gulfport Energy - The oil and gas exploration company fell after cutting its production guidance by 30 percent.
J.M. Smucker - The seller of Folgers coffee rose after Goldman Sachs upgraded the stock to neutral from sell. It also expanded its partnership with Keurig Green Mountain .
L Brands - The retailer rose after reporting April comparable sales rose 8 percent. It also raised its first-quarter earnings outlook.
Liberty Media - The communications company rose on news it would spin off its cable assets into a publicly traded company called Liberty Broadband.
PHH - The mortgage provider fell to an eight-month low after reporting weaker-than-expected first-quarter earnings.
Teradata - The data storage company fell after warning second-quarter revenue would fall.
Tiffany - The upscale jeweler rose after Bank of America/Merrill Lynch upgraded the stock to buy from neutral.
Twitter - The social media company and Yelp gained after Morgan Stanley raised its ratings on both.
Visteon - The auto parts maker advanced after reporting a 7 percent rise in quarterly revenue.
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—By CNBC's Rich Fisherman.
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