1. The Bitconnect Cryptocurrency Scheme - 2$ billion
At its height, Bitcoin was one of the most popular places for amateur investors to place their money in hopes of profiting extravagantly. Some were definitely able to, but those that had their money in Bitconnect ended up losing over $2 billion collectively within just a few hours.
Image source: pinterest
The cryptocurrency collapsed from a high of $331 to just $21 within six hours as major investors pulled out and the SEC tightened the noose on the scheme. Ultimately, the lack of new users meant they were burning through more money than they were making and had to bail.