How do social media sites make money?

[Vertical Reality]

Wikipedia is not for profit.

Almost all of their money comes from donations and pledges.

Facebook, Google and others get almost all their revenue off advertising. And it's also important to note that these companies are not profitable for a long time. I think it's only been recently that Facebook made an actual profit from their website.

They probably have other ways aside from advertising (though advertising is probably the largest) but you would have to look at each website on a case by case basis.

Oh and I forgot to add these sites also probably sell stuff like Google t-shirts (an example, I don't know if google actually sells t-shirts).