The latest study by PEW Internet states that social media use is still rising. On average now 65% of American adults are using social media.
Whereas the use is rising at all the graphs of growth for particular groups do show slight kinks. But most of these kinks are just temporarily. The ongoing growth of social media use is caused by some groups having adopted social media later than others. Typical groups having adopted social media later are inhabitants of rural areas and older people.
The study is accessible for free by the following link: Social Media Usage: 2005-2015