Then Musk’s account tweeted “Good Morning” with a smiley-face emoji at about 1:30 p.m. ET.
The stock jumped as high as $371.15 and then came back as traders began to question the legitimacy of the tweet. It was last at about $358, already up more than 5 percent on the day because of a report of a new stake from the Saudi Arabia sovereign wealth fund.
In the past year, Tesla shares have traded as low as $244.59 in April and as high as $389.61 in September.
Tesla went public in 2010. Its current market value is $61 billion. At a share price of $420, the company would be worth $71.3 billion.
Musk has said he expects Tesla to begin being profitable in the third quarter of 2018.
Taking Tesla private could remove some of the pressure on the closely watched company. For example, the electric car maker would no longer have to publicly report quarterly earnings.
Investors have been concerned about the amount of cash Tesla has been burning through and whether the company would need to raise additional funds to support its growth plans, which include introducing a semi-truck, a crossover SUV called the Model Y, more factories around the world, and other projects.
This story is developing. Please check back for updates.