The authors thank Sophie Hilgard, Victor Lei, and Yang Tang for input; Dean Eckles, Ali Goli, Solomon Messing, Donald Ngwe, Omid Rafieian, Yanwen Wang, Linli Xu, and Zikun Ye for extensive feedback and comments that have significantly improved the paper; and participants at the following seminars and conferences for helpful comments and suggestions: University of Michigan, Harvard University, the University of Toronto, the University of British Columbia, Lehigh University, Chapman University, Stanford University, William & Mary, Hong Kong University of Science and Technology, the Virtual Digital Economy Seminar Series, the UW-UBC marketing conference, the INFORMS Marketing Science Conference, the CODE@MIT Conference on Digital Experimentation, the Workshop on Platform Analytics, and the Interactive Marketing Research Conference. An earlier version of this paper was circulated under the title “Producer and Consumer Engagement on Social Media Platforms.”