The definition you are using is a very strict one, and is only really useful for comparing "market economies" to "command economies". That is clearly not what we are talking about here.

The definition I am using is of an "ideal free market", which is what is required for any of the "free market theory" consequences to come into play. That includes things like revealed preferences theory. An "ideal free market" requires no friction, perfect information, perfect elasticity, etc.

Without that, the idea that you can tell what people "really want" in social media based on which networks they use is completely false.