Seeing posts about How Do I Find My Friends, or Fedi Sucks Because I Can't Find My Friends, and... you ask them for their username. Text them or email them or give them a ring and ask them where they signed up and what name they chose.
It's in the format @username@server.tld, paste it into the search box and hit Follow.
I'm really honestly suspecting that some of these people who can't find their friends might be talking about, charitably, friends who might not know that they're friends. 😕
"How do I find my friends" is perhaps inaccurate. What I want to know is how do I find all the interesting and popular accounts that I have a parasocial relationship with.
I'm sure John Scalzi doesn't know me from Adam, but I enjoy his tweets. How do I find people like John Scalzi, Ken White or Kai Rysdal who have accounts somewhere in the Fediverse. (No not those three in particular. I know none of them are on here, but people like them who are.)
