Worked in Tech in Los Angeles since 2000. Although lesser known as "tech" companies, there are several companies that have large investments in serious technology in LA:
Disney
NBCU (specifically Fandango, parts of former M-Go)
Ticketmaster/Live Nation
eHarmony
Edmunds.com
The Honest Company
Other Tech companies left off the list:
Hulu
Yahoo (much smaller than before)
AOL
Hyperloop One and Faraday Future are coming up
Perhaps "media" is too broad a term. I think there's a concentration of certain types of industries - entertainment video, gaming, ecommerce, adtech, automotive, some fintech, some social media.
What there isn't a lot of is "engineering", "cloud", "enterprise" technology. The GitHubs, Herokus, AWSs of the world are not yet here in LA. For those of us who are engineering focused, we generally do tech for companies that don't "sell" technology to other engineers, that's focused in SF and Seattle. Not any less valid just a different audience.
Disney NBCU (specifically Fandango, parts of former M-Go) Ticketmaster/Live Nation eHarmony Edmunds.com The Honest Company
Other Tech companies left off the list: Hulu Yahoo (much smaller than before) AOL Hyperloop One and Faraday Future are coming up