Tesla's filed a SEC form 8-K[0] on 2013-11-05 that elevated both Musk’s and Tesla’s Twitter accounts to Disclosure Channels:
>Tesla Disclosure Channels To Disseminate Information
>Tesla investors and others should note that we announce material information to the public about our company, products and services and other issues through a variety of means, including Tesla’s website, press releases, SEC filings, blogs and social media, in order to achieve broad, non-exclusionary distribution of information to the public. We encourage our investors and others to review the information we make public in the locations below as such information could be deemed to be material information. Please note that this list may be updated from time to time.
>Interested in keeping up with Tesla?
>For more information on Tesla and its products, please visit: teslamotors.com
>For more information for Tesla investors, please visit: ir.teslamotors.com
>For the latest information from Tesla, including press releases and the Tesla blog, please visit: teslamotors.com/press
>For additional information, please follow Elon Musk’s and Tesla’s Twitter accounts: twitter.com/elonmusk and twitter.com/TeslaMotors
Tesla designated Musk's twitter account several years ago.