Social media have shown great potential for producing significant changes in behavior and have become the cornerstone for many public health and agency efforts. The nonprofit sector -including blood collection agencies- has adopted social media to aid their cause and reach their goals. However, despite the tremendous impact of social media on society and its promising role for donor recruitment and retention, it has been overlooked in donor research. This study therefore sought to map the social media landscape around blood donation. We showcase an inductive computational method to make sense of vast amounts of dynamic unstructured blood donation text data that exists on social media. With this method, we display what is discussed about blood donation on social media, how these topics are distributed on Facebook and Twitter, and how the prevalence of these topics changes over time. We applied structural topic modeling on 7 years of Dutch blood donation Facebook and Twitter data by the general public. We found 25 topics clustered in 6 distinct clusters. Over time, there is a substantial reduction of messages in which donors announce their donations. Topics that emphasize the positives of blood donation, including donor identity-related topics, are rising. In addition, the findings show a clear social media platform contrast. Topics related to campaigns and controversial policies were found more on Twitter and positive donation topics and topics related to the donation process more on Facebook. To make optimal use of social media for recruitment and retention campaigns and efforts, blood collection agencies should recognize the turbulent environment in which they take place. Monitoring public opinions about blood donation will help blood collection agencies make strategic choices and utilize social media more effectively.