Encyclopedias, along with textbooks, give good overview information about a client or population. They can help you determine the population most impacted by a social issue as well as relevant policies, timelines, and other important information to consider.
Search broadly for things like "substance use" or "adolescents."
Data sources help you build a case regarding the prevalence of a social issue among your chosen population or among the population as a whole. This shows evidence of the need for an intervention.
Perform a scoped Google search for statistical information online. Here's an example of a search that is limited to .gov webpages:
Search: Dallas homeless statistics site:gov