It's imprudent to decouple popularity from price. Would you invest in Facebook a $200b valuation? $500b? Popularity is already priced in by the market.

To invest, you need to have a fundamental belief about the long term prospects of the company above that of the market. I think better answers would be "I think Facebook is a $150b company, so yes" or "I am 50% more bullish on Facebook than the market" or "I think I will be able to sell to people in the future who will be 50% more bullish on Facebook at that time."