The URL of the Tokyo-based Mt. Gox was returning a blank page. The disappearance of the site follows the resignation Sunday of Mt.Gox from the board of the Bitcoin Foundation, a group seeking legitimacy for the currency.
Separately, several Bitcoin exchanges released a joint statement saying that funds under their control are held securely.
The Bitcoin operators said they are working to "re-establish the trust squandered" by the failings of Mt.Gox, which should not be considered a reflection of the value of Bitcoin or the digital currency industry.
A "crisis strategy" report shared widely online that purports to be an internal Mt. Gox document says more than 740,000 Bitcoins are missing from the exchange, which froze withdrawals earlier this month.
The cloud hanging over Mt.Gox is a possibly fatal blow to Bitcoin. Supporters of the virtual currency have said its cryptography makes it immune to theft or counterfeiting.
On Bitcoin exchanges, the currency's value has fallen below $500 from about $550 in the past few hours,
Bitcoin was started in 2009 as a currency free from government controls. It had been inching toward broader acceptance despite wild swings in value in the past year. For most of the currency's history, each digital coin had been worth less than $10.