Bandwagon Bias
The bandwagon bias refers to the tendency people have to adopt a certain trend-following behaviour or investment based on the perception that others are involved.
See madness of crowds, bubble and market mania.
References
- Leibenstein, Harvey. "Bandwagon, snob, and Veblen effects in the theory of consumers' demand." The quarterly journal of economics 64, no. 2 (1950): 183-207.