In an older article about social network trends, I discussed how Facebook in particular was far past its peak as measured by Google Trends. And that trend has not turned. There is a smaller and smaller fraction of web searches for the term "facebook". It is now around a similar level as in 2009. Some of this can be explained by the fact that more people use the Facebook mobile app to access the social network, and therefore do not need to search Google to access the site. However, as pointed out by this Guardian article, despite claiming 1.79 billion users, 2016 was the year Facebook "became the bad guy". In the Western world, interest was saturated several years ago, and new users come from other regions and possibly where Facebook have been blocked. They now plan to adapt their site and network to China's censor and surveillance requirements.
Yet, if you are an investor in the social network, you might want to hold on a bit longer before you sell. In recent years, Facebook has snapped up both of the new popular social apps Whatsapp and Instagram (in 2014 and 2012 respectively). They continue their upwards trend, and will do so for many years to come. Compared to Facebook they both pale on Google Trends, meaning there's a lot of potential.