It bears an Internet suffix originally assigned to the Soviet Union, and many of the pages feature unflattering pictures or taunting messages of the person featured. Others whose information is posted include pop star Britney Spears, Attorney General Eric Holder, former Alaska governor Sarah Palin and former California governor Arnold Schwarzenegger.
Both the FBI and the Secret Service said Tuesday they were investigating the site.
White House Press Secretary Jay Carney said he had "no assessments to offer" on the situation and referred questions to the Secret Service, which wouldn't provide further details.
The site grew from 11 names to 20 in the first 24 hours since it became public, with its operator adding additional features to count the number of visitors and a link to a Twitter account. It offers no explanation about why the targets were selected or how the information was obtained. The Twitter account includes an anti-police message in Russian.
Social Security numbers posted on Jay-Z, Mel Gibson and others matched records in public databases. Social Security numbers are not public records, although they used to be included in some court filings. Many courts require the information be redacted from filings since the numbers can be used to steal a person's identity and open credit accounts in their name.
President Barack Obama told ABC News that he was aware of the investigation into the possible breach of his wife's data.
"We should not be surprised that if we've got hackers that want to dig in and have a lot of resources, that they can access this information," Obama said. "Again, not sure how accurate but ... you've got Web sites out there that tell people's credit card info. That's how sophisticated they are."
Online security expert Marc Maiffret said sensitive information can often be gleaned from a single database, but the varied nature of the people targeted made the site's motives less clear.
Maiffret, the chief technology officer for Carlsbad, Calif.-based security firm BeyondTrust, said the site contained information that if accurate could be very damaging to its targets.
"Pretty much everything comes falling down once you have a Social Security number," he said. "Once somebody has that, the person has the keys to everything."
The information could be used to shut down accounts and utilities, although Maiffret said celebrities and government officials have more resources to protect themselves and their financial companies will likely be guarding their accounts in the wake of the site's postings.
Average consumers should consider adding a second password to their accounts to protect against hackers who have access to their Social Security numbers and other financial info.
Los Angeles police also are investigating, trying to determine how information was obtained, including the address and credit report of Police Chief Charlie Beck.
Beck told reporters Tuesday that detectives would work to bring anyone responsible for posting the info online to justice.
"We will vigorously pursue the individuals that have made me a victim and have made a number of other people that are in the public eye victims," he said.
He acknowledged that many hackers operate outside the United States, but said there is often a connection stateside that can lead to prosecutions.
Frank Preciado, assistant officer in charge at the LAPD online section, said the postings are illegal. He said the information on the police chief was likely taken from what is supposed to be a secure database of city employees.
The site's page on Beck includes a reference to former officer Christopher Dorner, who apparently committed suicide after he killed four people during a multi-day rampage. Beck's page included the message "YouCantCornerTheDorner" and an image of a woman protesting police corruption.