Robinhood users can’t get enough of Tesla Inc.

Almost 40,000 Robinhood accounts added shares of the automaker during a single four-hour span on Monday, according to website Robintrack.net, which compiles data on the investing platform that’s much beloved by day trading millennials.

The one-day return may not have turned out so well. Tesla was up as much as 16 per cent at one point before paring gains through the day and finishing three per cent lower. It was a rare losing day for the high flying stock, which has surged 56 per cent over the past 10 days.

All told this year, Tesla’s market cap has surged by US$202 billion, pushing Elon Musk past Warren Buffett in rankings of the world’s wealthiest people and burning shorts who have as much as US$20 billion in bets the stock will fall.

The stock is trading at 166 times estimated earnings over the next year, 20 times book value and seven times sales. The frenzy in interest means that as of the end of Monday’s trading session, there are now roughly 457,000 users on the Robinhood app that hold shares of the company in some form. That makes it the 10th-most popular stock on the platform, ahead of even Amazon.com Inc., which is held by 358,000 users.

It isn’t at all clear that day traders are the main driver for the nosebleed rally in Tesla shares over the past few weeks.

Indeed, there are myriad other possibilities, from the potential reveal of a new battery technology, to short covering, to conjecture over the possibility for the stock’s addition to the S&P 500 Index.

Of course, Tesla is just one company. But for those who like to track investor sentiment, particularly as a contrarian market indicator, the surge in interest Monday sure seems like a doozy.