[AlexandrB]

I disagree. The "algorithm" is fundamentally an optimization problem and companies get to choose what the fitness function for each algorithm is. Facebook chooses "engagement". This is not an accident nor some fundamental property of math. It's a product decision made by a human. One that can be changed.

And there is a fundamental difference between Google's algorithm and Facebook's: control. Google requires user input through search, Facebook decides what shows up when you open the app/site based on an algorithmic feed. In one case the user has some idea that what they're doing is interacting with an algorithm and they can change their search terms if they're not satisfied with the results, in the other the algorithm is in the background making decisions without making itself obvious.

[Gigablah]

There is an implicit search on Facebook though, namely the personal information you’ve entered into your profile and your relationships.