The idea that you can check someone's assets, such as bank and brokerage accounts, by means of a Social Security Number is a persistent urban myth. It's not that it can't be done in other ways, but with a few exceptions, it's illegal. There are other ways you can locate assets, with or without a SS number, but you have to be careful not to exceed your legal right to access this information.
Promises That Sustain the Myth
If you go online and google "check assets using a social security number," you'll find any number of private investigation ads offering to do just that. Is it legal? Like a lot of life's questions, the answer is "maybe" or "sometimes." One thing that's definitely true is that there's no magic online source into which you can plug a SS number and come up with a list of assets. That doesn't exist. Under the 1974 Privacy Act, Federal agencies may not disclose information without consent unless certain exceptions apply to the disclosure.
However, for trained investigators, coming up with asset locations and amounts isn't particularly difficult. In our everyday life we leave a trail of information breadcrumbs behind that establishes a lot of asset and SS information: job applications, credit reports, legal proceedings – especially divorce proceedings – public records and mortgage applications among them. Even if the investigator begins without a subject's SS number, it's there on your credit and job applications anyway, so getting it's hardly a big deal. Armed with all this data, an investigator can usually determine the locations and at least the approximate asset amounts.
But if you contact these firms, you'll also discover (assuming they want to keep their PI licenses) that you can't just waltz into a PI agency and pay it to get information on someone because you're curious. You need a good reason for obtaining this information.
What Are Good Reasons?
There are several good reasons for wanting to know. You're getting divorced, for example, and you think your spouse's declaration of assets is untruthful. Or you're owed child support or have an outstanding court judgment against someone who has declared he's insolvent.
Underlying most searches conducted for such reasons is a court order allowing it. Without a court order, the investigator can legally go only so far. He can determine the existence and location of a bank account, for instance, but cannot legally access the account itself to come up with an exact amount. On the other hand, most experienced investigators can come up with surprisingly accurate informed guesses. Armed with a court order, however, the investigator has a potent right to open all known channels of information, including Federal records and, yes, each and every bank and brokerage account.