1. Does the statistic exist? It may not have been collected.
2. Has the statistic been released yet? It takes time to collate and organize statistics. Often there's a time lag between the collection of statistics and when they're released or published.
3. Who might have produced the statistic? For example, if it's about an industry, is there a relevant industry association that might have collected the statistic?
4. Are you using the right keywords to search? Use alternative words to search. For example, if you have not found any statistics using the keyword 'teenagers', try using the word 'adolescents' instead.
5. Is there a relevant Wikipedia page? Take a look at any statistics on the page and refer to the source of the statistics.
Commercial statistics, especially those that would give one company a competitive edge over another are hard to find for free. This includes market research data, brand sales, and some financial statistics.
Research journal articles or conference proceedings often carry statistics, charts or graphs to back up arguments, as well as the results of surveys or questionnaires.
Library databases have lots of information from journal articles or conference proceedings. Some, such as EBSCO Library database allow you to limit your search results to publications that contain statistics.
The image below, from EBSCOhost shows options to find journal articles that have charts or graphs.