Midday Report: Snap Advances Again; U.S. Stocks Wait for Remarks From Fed's Yellen

Stocks moved lower as investors played it safe ahead of an afternoon speech from Federal Reserve Chair Janet Yellen. Yellen could signal a rate hike as soon as this month. Snap (SNAP) - Get Report advanced again in day two as a public company. The disappearing message app currently has a market cap nearly three times larger than social media network Twitter (TWTR) - Get Report and even slightly more than traditional media company CBS (CBS) - Get Report . GNC (GNC) - Get Report shot higher on reports private-equity firm KKR is interested in a deal. KKR has reportedly been in contact with two Chinese companies over a potential acquisition of the vitamins retailer. Services activity in the U.S. strengthened in February, according to the latest reading from the Institute for Supply Management. The uptick in the ISM non-manufacturing index was a surprise to analysts looking for it to hold at January levels.