Tesla Share Price Slides After Musk Promises to Sell $21 Billion Stake

Tesla Inc. shares fell in premarket trading after Twitter users directed Chief Executive Elon Musk to sell a 10th of his stock in an online poll.

The electric-vehicle maker’s stock lost 5.2% in brisk trading ahead of the bell Monday. Tesla shares changed hands more than 700,000 times, according to FactSet, more than any other stock on the S&P 500. “I was prepared to accept either outcome,” Mr. Musk said in a tweet Sunday after participants in the poll backed a sale by 58% to 42%. Neither Mr. Musk nor Tesla has said when a share sale would take place.