If someone found your Bitcoin private key, that person probably used that key to sign a transaction to one of his Bitcoin addresses (accounts). There is no way for you to actually recover them. You could however track the transaction to eventually see where your bitcoins are being transferred.
Now if your Bitcoins are stored at a company such as an exchange or a cold storage company, you might have some kind of insurance that the company provides as they're responsible of keeping your bitcoins safe.