This comment seems to be downvoted which is disappointing, as this is one of the best pieces of advice here. Apart from when I was a fresh graduate, all of my jobs and contracts over the past 10 years have been from networking.
I'm definitely not a people person, and you don't need to be, you just need to keep up to date with what people in your network are doing. If there is anyone now in a management role, try to meet up with them for a coffee once a year just to chat. Maybe they are looking for someone with your skills (that's happened twice for me). I've also been in the situation where they aren't actively looking for someone, but knowing that I'm available and that I do good work they've made a position just for me.
I've only worked at smaller companies, so I'm not really sure how this would work at the scale of something like Facebook, but other than them having to navigate HR I don't see why it couldn't work.
I'm definitely not a people person, and you don't need to be, you just need to keep up to date with what people in your network are doing. If there is anyone now in a management role, try to meet up with them for a coffee once a year just to chat. Maybe they are looking for someone with your skills (that's happened twice for me). I've also been in the situation where they aren't actively looking for someone, but knowing that I'm available and that I do good work they've made a position just for me.
I've only worked at smaller companies, so I'm not really sure how this would work at the scale of something like Facebook, but other than them having to navigate HR I don't see why it couldn't work.