Even assuming only DAUs would pay $1000/year (Facebook has 1.5 billion of them) and a P/S ratio of 1 (which is conservative), the company would be worth $1.5T.
Edit: But we should consider something like Metcalfe's law, as pointed out by berbec
Edit: But we should consider something like Metcalfe's law, as pointed out by berbec
Giving, in this case, a value of $750B (at a P/S ratio of 1)
https://www.wolframalpha.com/input/?i=Sum%5Bn+6.67e-7,+%7Bn,...