It isn't "air". It's an advertising and media device. Depending on what you read they currently employ around 3500 people, but have been planning on acquiring facilities for as many as 6000-10000 US-based employees. That doesn't include the various companies and their employees that generate revenue by providing access to FB (ISPs, mobile device manufacturers, service providers, etc). No doubt they also have real estate and other properties to house their offices, servers, etc. Over the years they've acquired nearly 30 other companies, some were quite valuable on their own - they have assets.
Current estimates show they have over 400 million users online <span style="font-style: italic">daily</span>. Just like television, Facebook is primarily an advertisement-delivery tool and as such have value.
I'm not particularly a fan of Facebook, but it's hardly "air".