In this study, we closely look at the use of social media contents as source or reference in the U.S. news media. Specifically, we examine about 60 thousand news articles published within the 5 years period of 2013-2017 by 153 U.S. media outlets and analyze use of social media content as source compared to other sources. We designed a social media source extraction algorithm and investigated the extent and nature of social media source usage across different news topics. Our results show that uses of social media content in news almost doubled in five years. Unreliable media outlets rely on social media more than the mainstream media. Both mainstream and unreliable sites prefer Twitter to Facebook as a source of information.