Some data from an interview with Prof. John Cacioppo, the director of the University of Chicago’s Center for Cognitive and Social Neuroscience and author of Loneliness: Human Nature and the Need for Social Connection (W. W. Norton & Co., 2009)
http://fortune.com/2016/06/22/loneliness-is-a-modern-day-epi...
"I’ve seen studies that suggest the percentage of Americans who report chronic feelings of loneliness has risen over the past few decades.
Looking from a few different sources of data, it seems that way. The percentage of Americans who responded that they regularly or frequently felt lonely was between 11% and 20% in the 1970s and 1980s [the percentage varied depending on the study].
In 2010, the American Association of Retired Persons (AARP) did a nationally representative study in 2010 and found it was closer to 40% to 45%. And a recent study done on older adults out of University of California - San Francisco put it at 43%. In our own longitudinal studies, we’ve seen it at about 26% and longitudinal studies in Europe have found around the same thing; there could be mathematical reasons for why it’s lower in longitudinal studies than in cross-sectional studies ones.
So loneliness levels are on the rise, we’re just not sure by how much. Why do you think this is the case?
We aren’t as closely bound. We no longer live in the same village for generations, which means we don’t have the same generational connections. That releases social constraints—relationships are formed and replaced more easily today. We have Tinder, Match, eHarmony and all these kinds of places you can dial up and find friendships, connections and opportunities that didn’t exist. In the last 15 years or so, many of those face-to-face connections have been replaced with social networking.
We’ve found that if you use social networking as a way to promote face-to-face conversation, it lowers loneliness. But if you use a destination, as a replacement for the face-to-face, it increases loneliness."
Interestingly, a paper found evidence for declining loneliness among American college and high school students.
https://www.ncbi.nlm.nih.gov/pubmed/25422313
If I need to guess I'd say that online social networking may promote face-to-face socialization among students, while it is often used as a replacement for in-person interactions among older adults.