Amazon stock plunged 8% in premarket trades Friday. The e-commerce giant reported second-quarter results that topped Wall Street's expectations, but gave a mixed outlook. For the current quarter, Amazon predicted sales of $176.75 billion at the midpoint of its range, compared with analyst expectations for $173.27 billion.

The last day of a busy week ends with the first greater-than-1% move in either direction in more than a month.