No you can't own a platform like youtube or facebook, but you could make content on it, intellectul propriety is not a thing as you don't have to produce art just to get a monetary return, but just because you enjoy doing so, there's no need of a stock market in an ideal communist world because everyone gets what they need based on what they can provide, but if it's just a country i guess it's the government who takes care of it.

Regarding those 5 countries i'm not sure of every one of them, but talking about China as you said it's not a communist country but it is not a dictatorship of the proletarian either, as it's not the proletarian class nor their democratically elected representatives who govern the country.

In the end i'll add that greed is not more "human nature" that wishing to kill someone annoying.