Earlier quoted context omitted.
Quitting Facebook doesn't cure the social bankruptcy, though. The only cures seem to be joining cults and gangs and militaries and other groups with high costs and low standards.
You develop social capital by fostering relationships with other people. By being responsible, and having positive interactions. You'll develop that capital not just with them, but also with the people around you and them. If you have a positive relationship with someone, and they think well of you, then their friends and family and colleagues will accept their voucher (assuming they have a positive relationship with…
I had to go through a similar process starting from nearly zero, and it was not easy. I did it by running D&D, as everyone around wants to play a game, but nobody wants to go through the effort of running one. All of the above advice applies.