Opendoor Technologies, a penny stock last week, attracted sudden interest among Reddit-obsessed retail traders, who pushed up the stock price by threefold in days.The online real estate startup saw shares popping more than 18% Tuesday,

The online real estate developer's shares are on a stellar run. Investors should be careful not to get burned.

Opendoor stock took off last Monday after Eric Jackson, founder of EMJ Capital, announced his firm had taken a position in the company and said the stock “could be a 100-bagger over the next few years.” The term refers to stocks that return $100 for every $1 invested.