Twitter CEO Dick Costolo was a big-name speaker at CES on Wednesday, but his appearance at an uneventful panel discussion was upstaged by a second consecutive steep drop in the company's young stock. Twitter shares slid 3.5 percent to $59.29, completing a two-day decline of 10.6 percent, after another analyst said that the steep run-up in Twitter's valuation at the end of 2013 made little sense. "We find Twitter's valuation to be excessive and currently see materially more downside than upside," Cantor Fitzgerald analyst Youssef Squali wrote in downgrading the stock Wednesday morning, though he noted that it was because of the price and not any structural defects within the company.