(May 18): Elon Musk’s Twitter posts keep sending Bitcoin prices tumbling. His own fortune is heading in the same direction.

On Monday, Tesla Inc.’s chief executive officer lost his spot as the world’s second-richest person to LVMH Chairman Bernard Arnault as the electric vehicle-maker’s shares fell 2.2%. That was on top of last week’s slump amid a global rout in technology stocks and fresh signs of trouble in its China business.