The only money accepted on Silk Road was the digital currency bitcoin, which was meant to add an additional layer of anonymity to buyers and sellers.
Over the past two and a half years, the FBI said the site generated revenue worth more than 9.5 million bitcoins -- valued at roughly $1.3 billion.
British police said millions of pounds worth of bitcoins had been seized in the operations against Silk Road, and they were working with other countries to investigate the threat presented by virtual currencies.
Silk Road wasn't just used for dealing in illegal drugs. The FBI says it was also used to trade firearms, hire assassins and employ hackers.
The FBI had worked on shuttering Silk Road and tracking down its creator since late 2011. For the investigation, the FBI teamed up with the IRS, Drug Enforcement Administration and an investigative unit of the Department of Immigration and Customs Enforcement.
--CNNMoney's Jose Pagliery contributed to this report.