Nasdaq-100 tumbles 2% as Facebook continues to weigh

The Nasdaq-100 slumped on Thursday, putting the index of large-capitalization stocks traded on the exchange on track for its seventh decline of the past eight sessions. The index NDX, -2.04% sank 2.1%, and is down 4.4% thus far this week. According to FactSet, the PowerShares QQQ Trust QQQ, -2.10% the largest exchange-traded fund to track the index, has seen $1.4 billion in outflows over the past week. That represents some of the highest outflows of any stock-based ETF over that time period. Recent weakness in the index has largely come on the back of Facebook Inc. FB, -2.64% The social-media giant fell 2.4% on Thursday, extending a period of weakness that could represent its biggest one-week decline in about four years. Facebook, a major component of the Nasdaq 100, has been enduring a firestorm and stock selloff after data-mining company Cambridge Analytica reportedly used the personal details of 50 million Facebook users without authorization. On Wednesday night, Facebook CEO Mark Zuckerberg apologized for the controversy during an interview with CNN, and said he'd be willing to testify before Congress. The Dow Jones Industrial Average DJIA, -1.87% fell 1.9% while the S&P 500 SPX, -1.70% was off 1.8% and the Nasdaq Composite Index COMP, -1.88% was off 2%.