One of the reasons that certain advertisements are successful is because viewers want to behave like those they observe. What is the general term that psychologists use to describe this type of behavior?

One term is beautiful people.

http://en.wikipedia.org/wiki/Propaganda_techniques

The general term that psychologists use to describe the behavior of wanting to emulate or imitate others that one observes is called "social imitation" or "observational learning." It is a cognitive process in which individuals learn by observing the behavior of others and imitating their actions. This concept is often associated with the theory of social learning developed by psychologist Albert Bandura.

To find this answer, you could conduct a search using appropriate keywords such as "psychology of advertising and social imitation" or "observational learning and consumer behavior." This will help you find relevant sources, research articles, or psychological theories that discuss the influence of social imitation on advertising effectiveness.