Appeal to popularity
According to Discovering the World through Debate, an "appeal to popularity" is "A fallacious argument that occurs when a debater uses the popularity of a person, product, or belief to justify a favorable conclusion about that person, product, or belief" (246).
Trapp, Robert, et al. Discovering the World through Debate: A Practical Guide to Educational Debate for Debaters, Coaches, and Judges. Third Edition. New York: IDEA Press Books, 2005.