Utilizing social media celebrities as a communication channel has become a strategic practice for many organizations. By using the concepts of celebrity endorsement and authenticity, the effect of celebrity and content characteristics on followers’ attitudes towards the content and, in the case of sponsored content, purchase intentions are scrutinized. Instagram followers (N = 592) of 45 celebrities responded to a survey on nine photos of the celebrities. The results show that both the perceived authenticity and attractiveness of the celebrity are positively related with photo attitudes, but only authenticity has an effect on purchase intentions. Photos of social media influencers, people who have become famous through social media, increase purchase intentions more than photos of general celebrities. Congruence between the photo and the celebrity has the strongest positive effect on photo attitudes and purchase intentions. Sponsored photos are less favorably perceived than non-sponsored photos, but, among sponsored photos, sponsor disclosure has no effect on purchase intentions. The perceived authenticity of both the celebrity and her content is said to explain favorable audience perceptions. The findings imply that organizations should seek authentic matches between their message and the endorsing celebrity and that the content should align with the usual style of the celebrity.