Social Media Platform - what backend lang would you use? (Don't know if these are the large/standard langs).

So, if you were to build a social media platform with billions of accounts - what kind of backend would you use?
I'm partial to PHP/Laravel and I don't facebook use this. But Go has been getting great traction in the community and is quite a fun language.
How do all these hold up from a security perspective?
Which is easiest to use/grasp?
How future proof are they?
Any other kind of stuff I'm missing?