Previous research has analyzed the extent to which the structural characteristics of news organizations and the outlets where journalists operate explain differences in media diversity. Based on a content analysis of 16,281 news stories from Chilean television, radio, print, online media and Twitter, this study examines whether differences in source diversity remain stable across news media platforms within the same medium. The findings show that both platform type and medium significantly influence the presence of source diversity at different levels. Our results speak to the strong influence that each media platform has on how journalists manage news balance and number of sources when producing a story. They also provide strong evidence of the importance of the macro organizational structure of the medium for the type of sources included in the news. Likewise, our study questions common assumptions as it reveals that online media do not favor the presence of a greater diversity of sources and points of view in the news and are associated with a lower degree of diversity in general.