Answer: Yes, a case study would be an appropriate first step
Explanation: A case study will give him the necessary data and information needed to develop the hypothesis.
He would need to determine the sample size he wants to work with (the number of teenagers), the exact city of the country he wants to use for the study. Also, would he want to use both sexes (male and female)? Carrying out a case study after answering these questions would make the hypothesis valid since it is an objective means.