The report was based on data from a survey conducted in January 2018 among a nationally representative sample of 2,002 people age 18 and older living in the United States.
Some 73% of respondents say they use YouTube, and 68% of respondents say they use Facebook.
None of the other social platforms measured by Pew in the survey are used by more than 40% of Americans.
There are major differences in social media use by age, the survey found.
Some 88% of 18-29-year-olds use social media, compared with 78% of Americans age 30-49, 64% age 50-64, and 37% age 65+.
Americans age 18-24 are significantly more likely to use platforms such as Snapchat, Instagram, and Twitter, even compared with Americans in their mid- to late-20s.
For example, some 78% of 18-24-year-olds use Snapchat, compared with 54% of 25-29-year-olds.
Facebook users are the most active among the social networks examined.
Some 74% of Facebook users say they visit the site daily, with 51% saying they do several times a day.
Some 73% of respondents use more than one of the eight social networks included in the survey.
The typical (median) adult uses three social networks, though there are significant differences among age groups. For Americans age 18-29, the median number of social networks used is four, compared with just one for Americans age 65+.
Most users of various social platforms say they also use Facebook and YouTube.
About the research: The report was based on data from a survey conducted in January 2018 among a nationally representative sample of 2,002 people age 18 and older living in the United States.