Tesla Inc.’s share price sank to near its lowest point for the year Friday after the electric-car maker lost more executives and Chief Executive Elon Musk appeared to smoke marijuana during an interview streamed on the web.

Dave Morton, touted by Tesla in late July as part of “key new talent” hired after a spell of executive departures, said Friday in a filing that he left because the public attention on the company and its pace were too much. Tesla also confirmed that Gabrielle Toledano, its head of human resources, wouldn’t...