Likewise, Facebook most probably couldn't find another company(s) to purchase the other $14.76B of it's stock anytime soon (do you think they could?).
By the way, it's also important to note that when you use the phrase, "on paper," it implies an unrealized gain. In the case of an investment valuation without any true financial backing (like in this case where we have a $15B valuation without $15B actually existing), there is no realized or unrealized gain.
So, even saying he's a billionaire "on paper" would be incorrect.
At best, since he controls about 1/3 of the $240M investment, he has $80M "on paper."
First, the article said: "The deal makes geeky twenty-three-year-old Mark Zuckerberg, at least on paper, worth $5 billion."
If the valuation is meaningless, feel free to take that up with the author of the article. Furthermore, I never said they could sell the company for $15 Billion. My comments were based solely on the article.