This seems implausible just on the face of it: that's almost a tenth of all Bitcoins created. How could they have lost that much and continued functioning at all? How could no one have noticed the bleeding in the blockchain? etc
I suppose if it happened over a long enough time and Gox's accounting system was truly terrible they could have just thought they were experiencing a bank run.
But yeah, I'm very skeptical.
This is most likely an attempt to manipulate the market. Not only are they suggesting Mt Gox is insolvent, but Bitcoin's existence is threatened.
Don't believe everything you read on the internet.