I'd be more than happy to know "your" expected growth rate. Facebook has not disclosed its business plan, views on the online ad market, ongoing capital expenditures and working capital needs.
Who's failed to provide future growth information is Facebook, not the other way.
More importantly, the Tech audience keeps looking at P/E as a valuation metric, but what rigorous and top asset managers do is look at Free Cash Flow to Equity, not Net Income. On a FCF to Equity valuation, FB IPOed at +220x.
Even at a generous P/E or FCF/E ratio of 25x, Facebook's Free Cash Flow needs to go from $450m to $4,000m in the next 24-36 months. Do you think that is possible? After looking at their infrastructure needs I think not.
I think it's you who has failed in the calculations.