The decline is putting the market on track for its first weekly loss in a month.
The Dow Jones industrial average fell 116 points, or 0.7 per cent, to 15,439 shortly before noon Eastern Daylight Time Friday.
The Standard & Poor's 500 index fell 10 points, or 0.6 per cent, to 1,679. The Nasdaq composite fell 13 points, or 0.4 per cent, to 3,592.
Expedia plunged 27 per cent to $47.62 after the online travel agency reported that its second-quarter profit fell by a third and badly missed Wall Street expectations.
Zynga dropped 16 per cent to $2.93 after the company said it was dropping its plans to pursue online casino-style games.