The response clearly implies the absurdness of using Google search trend as a tool for concluding Facebook user growth to reduce by 80% of current users in 2017. Below are some less satirical observations on the study and Facebook growth:
Google as a search tool for 'Facebook' stuff
Although Google search is the dominant search tool for most things out there, it is not surprising that searching people and pages in Facebook, is on the decline as found out by the Princeton team. The main reason behind this can be contributed due to the ascending Facebook user adoption and using Facebook itself to do such types of searches. Google as a search tool for many other category of searches is also on the decline, e.g., Twitter is more useful for trending news, Amazon for products, etc. More on the subject of not using Google for such kind of searches captured well by Mark Cuban here.
Facebook recent growth numbers
Although there is a lot of merit to the teenagers moving to other services like SnapChat, Instagram ,etc, there is no indication based on recent growth of any real overall user decline as can be seen in below chart
Facebook user growth opportunities ahead
Facebook has big ambitions on getting the lion's share of the remaining world population on it's social network and is focused towards achieving that goal. The leadership has already executed well on various challenges including bringing over 1 billion users to it's platform and supporting the daily activities of such a large group, moving to mobile successfully, and the more recent monetizing of the platform with lots of care on user retention. It will not be surprising to see Facebook further grow based on the management team credibility.
My conservative prediction of Daily Active Users on Facebook by 2017 year end based on a conservative 10% growth : over 1 billion
Disclosure: I am long FB.