It could be true but how come snap chat is worth so much and not what's app. Is it because they have actual revenue model while snapchat's value is speculative?

It could be true but how come snap chat is worth so much and not what's app. Is it because they have actual revenue model while snapchat's value is speculative? I don't really understand how valuations work. I read somewhere that they intend to make money by flash sales which I think is a really good idea for low priced products but it is not clear if they will make the money off transaction or allowing the product to be sold on their market place. It would be great if investors could shed some light on what they think is so valuable about the company in which they are investing so much.