The S&P 500 was down 0.3%, the Dow Jones Industrial Average slipped 0.08%, and the Nasdaq fell 0.62%.
Facebook reported a better-than-expected third quarter on its top- and bottom-lines. The social network earned an adjusted $1.09 a share, 12 cents above estimates. Revenue surged 56% to $7.01 billion, inching past consensus by $90 million. Total daily active users rose 17% to 1.18 billion, while mobile active users surged 22%. Mobile advertising now accounts for 84% of total ad revenue, up from 78% a year earlier.
However, shares fell 6% as growth concerns spooked investors. Facebook warned that advertising growth would "come down meaningfully" once it stops increasing the number of ads in users' news feeds. Facebook has increased ad volume over the past two years to drive revenue growth.
Fitbit shares crashed 30% after third-quarter sales missed expectations and its fourth-quarter outlook came in short consensus. The fitness wearables company reported a 23% jump in revenue to $503.8 million, but missed estimates of $506.9 million. Fitbit anticipates fourth-quarter eadjusted earnings between 14 cents and 18 cents, well below consensus of 75 cents a share. Full-year earnings guidance was nearly half what analysts had expected.