What do they do?
There are plenty of things to do in the company. For one thing, they have to have a bunch of people trying to convince advertisers to buy space. I assume that's the main reason to have a bunch of scattered offices; they have to have the people selling the ads where the buyers are. They also have a bunch of developers working on new features, like their new "moments" thingy, and presumably on better ways of targeting their ads. Finally, they have to have customer service and support people to do things like responding to abuse complaints.