No, not quite. They're funded by venture capitalists, who put money into investment rounds on the understanding (speculative gamble?) that the company will have a given future value. The last funding round was $6.6bn on the basis that the company will be worth $157bn when it is floated on the stock market. Ed Zitron has quite a good analysis on his page, and also why their business is a complete pile of shite:
They can say what they want, but investors won't invest if the ask is too high. These valuations are based on purchase of a given percent of shares, so you take the amount raised and divide by the percent sold and you get a valuation (a little more complicated than that, but that's the gist).