Update (9:34 a.m.): Updated with Wednesday market open information.
The stock was down 12.41% to $37.33 at 9:34 a.m. on Wednesday.
Zuckerberg calls Musk's doomsday interpretation 'pretty irresponsible.' Musk calls Zuckerberg's understanding 'limited.'
Twitter said that the incident was an accident.
One leading tech analyst says YouTube is worth 'at least' $75 billion.
News site ATTN: and ABC will use ABC News' footage and equipment to produce stories audiences will find appealing.