News—real or fake—is now abundant on social media. News posts on social media focus users’ attention on the headlines, but does it matter who wrote the article? We investigate whether changing the presentation format to highlight the source of the article affects its believability and how social media users choose to engage with it. We conducted two experiments and found that nudging users to think about who wrote the article influenced the extent to which they believed it. The presentation format of highlighting the source had a main effect; it made users more skeptical of all articles, regardless of the source’s credibility. For unknown sources, low source ratings had a direct effect on believability. Believability, in turn, influenced the extent to which users would engage with the article (e.g., read, like, comment, and share). We also found confirmation bias to be rampant: users were more likely to believe articles that aligned with their beliefs, over and above the effects of other factors.