Anyone, government or individual, has the capability to track bitcoin transactions. It's inherent to the blockchain. All of that information is public. There is nothing for the government to disclose. Your link talks about forensic efforts to unmask the owners of bitcoin wallets, which is a different animal.

The federal investigators only care about the transactions if you are doing something illegal. If you are simply investing in bitcoin, or using it to purchase goods/services legally, then you have nothing to worry about. And if someone uses their bitcoins to commit a crime, it is not going to affect the value of your bitcoins.

And the US Government considers virtual currency as property for tax purposes. Meaning, you can incur capital gains or losses when you dispose of your bitcoins, just like stock, etc. So exactly like I said, any gains are taxable and you must report it. This classification doesn't make it more "seize-able". But again, if you aren't doing anything illegal, you have nothing to worry about in this regard. No one is just going to seize your bitcoins because the Yakuza are involved.

There are still plenty of risks associated with investing in bitcoins, but I'd suggest doing a lot more research and make sure you understand the underlying technology before sinking any real money into it.