Final answer:
The available information does not provide an accurate percentage of teenagers in the U.S. using social networking websites.
Step-by-step explanation:
In a recent survey, it was found that 73 percent of adults engage in some form of social networking online. While this data specifically refers to adults, it provides some insight into the general usage of social networking sites.
However, to determine the percentage of teenagers in the U.S. using social networking websites, more specific data related to teenagers would be needed.
Therefore, based on the available information, we cannot accurately determine the exact percentage of teenagers in the U.S. using social networking websites.