The market was mixed on Thursday, with the Nasdaq Composite posting a modest gain while the Dow and S&P 500 stayed almost unchanged on the day. Events in Europe, including the U.K. election and a decision from the European Central Bank to keep interest rates stable, drew attention from international investors, but those in the U.S. didn't have a major response to those or other political events going on both domestically and across the globe.

Still, despite the quiet mood on Wall Street, some stocks suffered from bad news, and Sina (NASDAQ:SINA), Eldorado Gold (NYSE:EGO), and NewLink Genetics (NASDAQ:NLNK) were among the worst performers on the day. Below, we'll look more closely at these stocks to tell you why they did so poorly.

Sina slides on planned Weibo distribution

Shares of Sina fell more than 4% after the Chinese online media company detailed its plans to distribute a portion of the shares of microblogging specialist Weibo (NASDAQ:WB) that it still owns. Sina said that it will distribute one Weibo share for every 10 shares of Sina that investors own, leading to the distribution of roughly 7.14 million shares of Weibo. The distribution will take place on July 10, and it will reduce Sina's stake in Weibo from about 49% to 46%. However, Sina will retain voting control of Weibo, with the microblogging company's multiple share classes giving the online media player about 72% in terms of voting power. Weibo has been a big part of Sina's success, and some likely don't want to see Sina's stake in Weibo decline. Some of Sina's weakness also likely stemmed from the recent success of a key rival in the Chinese internet and e-commerce space, as rising competition will force Sina to up its game in order to keep pace.

Skouries processing plant.

Image source: Eldorado Gold.

Eldorado to go to arbitration

Eldorado Gold stock lost 9% in the wake of news that one of the company's projects will likely become the subject of arbitration proceedings. Reports from Greece indicated that the head of the Greek energy ministry will ask the nation's litigation specialists to make preparations for arbitration over a gold mining project that Eldorado is seeking to develop in the northern part of the country. The Skouries project is a high-grade gold and copper deposit on the Halkidiki Peninsula, and Eldorado is looking to operate the company as an open pit mine for the first nine years, followed by an additional 15 years of underground mining. The Greek government wants to ensure that Eldorado will make good on its contractual obligations, but Eldorado is still hopeful that development will allow for operations to start on the open pit portion of the project by 2019.

NewLink loses a partner

Finally, shares of NewLink Genetics plunged more than 40%. Roche Holdings said that it had decided to stop working with NewLink on the cancer drug GDC-0919, returning its rights to help co-develop the candidate treatment back to its smaller partner. Many investors were surprised by the move, but early study results seemed to indicate only marginal benefits from adding NewLink's treatment to existing drugs in Roche's stable. With competitors' drugs apparently providing greater benefits, Roche chose to pull the plug. For NewLink, the news comes only days after poor study results on another candidate treatment for breast cancer, and shareholders have to wonder when the bad news will turn around for the company. For now, investors seem downbeat on NewLink's prospects going forward.

Dan Caplinger has no position in any stocks mentioned. The Motley Fool recommends Sina and Weibo. The Motley Fool has a disclosure policy.