Donald Trump's stake in his social media company has gotten less valuable as the stock has fallen. But Trump's shares are still worth $2.4 billion.Anna Moneymaker/Getty ImagesShares of Trump Media & Technology Group — the company that runs Trump's Truth Social app — have plummeted.Trump Media/Truth Social is a meme stock, so that's not a total shock.But there are two good reasons why the stock could be under pressure right now.Earlier this year, Donald Trump's social media company was worth something like $9 billion.But that was then, and its stock has been sinking since: Now investors think Trump Media & Technology Group Corp — the company that runs Truth Social, Trump's Twitter clone — is worth a mere $4 billion.