As a teen on LiveJournal, I DEFINITELY invented a boyfriend. It was like fanfiction, but of my own life.
I have a frenemy who I wish I could stalk, but her profile is private. So I stalk her best friend (who has a public profile) literally all the time. I have to constantly clear my search history so as not to be conspicuous.
In the middle of chatting with a crush on AIM, I'd set an away message that said "in the shower!!" because I thought that would make him think of me naked.
My childhood BFF and I made a fake Facebook for a boy to make her then-bf jealous. To this day I feel very uncomfortable (yet proud?) when Facebook tells me it's "Noah Matthews'" birthday.
I obsessively checked the page of a girl I fancied who I found through a girl who was also obsessed with her on Tumblr. Actually started talking to her and she ended up moving from Denmark to London. We've been together 4 years and are now engaged!