NEW YORK ( TheStreet) -- Amazon > ( AMZN) stock sold off immediately after fourth-quarter earnings results, as profit topped estimates but sales missed. During the quarter the e-commerce giant earned $416 million, or 91 cents a share, on revenue of $12.95 billion. Analysts were looking for a profit of 88 cents on revenue of $13.01 billion. Margins also took a hit coming in at 3.7%, as Amazon amped up its investment in its infrastructure. Wall Street predicted margins of 4.2%. Once again, Amazon did not disclose sales on its popular Kindle e-reader. But CEO and Founder Jeff Bezos said the device helped push sales above $10 billion for the first quarter ever. "Kindle books have now overtaken paperback books as the most popular format on Amazon.com," Bezos said in a statement. "Last July we announced that Kindle books had passed hardcovers and predicted that Kindle would surpass paperbacks in the second quarter of this year, so this milestone has come even sooner than we expected -- and it's on top of continued growth in paperback sales." Shares of Amazon plunged 9.8% to %166.45 in after-hours activity. --Written by Jeanine Poggi in New York. >To contact the writer of this article, click here: Jeanine Poggi. >To follow the writer on Twitter, go to http://twitter.com/jpoggi. >To submit a news tip, send an email to: email@example.com.