Tesla CEO Elon Musk. It’s looking like another bad day for Silicon Valley billionaires. (AP Photo/Evan Vucci, File)

It’s looking like another bad day for Silicon Valley billionaires Elon Musk and Mark Zuckerberg.

Musk’s fortune dropped by $1.5 billion Friday in New York, the day after the Securities and Exchange Commission accused the Tesla Inc. CEO of misleading investors with his infamous tweet last month about taking the electric-car maker private. In its lawsuit, the SEC is also seeking to ban him from serving as a director or officer.

Meanwhile, Zuckerberg’s net worth fell about $2 billion after Facebook Inc. said Friday that it discovered a security breach earlier this week that affected almost 50 million of the social media giant’s accounts.

Shares of Facebook declined 2.7 percent to $164.28 in New York. Tesla shares dropped 13 percent to $267.38, and have tumbled 29 percent since Musk’s Aug. 7 tweet saying he had financing arranged to take the company private at $420 a share.

Musk’s net worth has fallen more than $4 billion since last month, putting his fortune at about $21.6 billion, according to the Bloomberg Billionaires Index. Facebook co-founder Zuckerberg’s worth about $64.6 billion, according to the index.