How do you end it?  Do you think it's okay to use social media for this purpose?

not something I have ever agonized over to tell you the truth. Friends come and go for a myriad of reasons. IMO the simplest knowing 'when to to end' is when there is no friendship to hold on to. 
In this techie age- using social media sites such as Facebook to let another human being know you want nothing more 3to do with them is cowardly so if I had to pick any choice given in the article it would be #1 or2 depending on the circumstance.

okay to use social media for anything private & personnel, think that a lot of people have learned their lessons. 

I lived in a community for many years. When I moved away  I stayed in touch with friends there. We visited back and forth occasionally. I'm good at staying in touch with people. It gradually got a bit one-sided, that is, I was the one always  initiating  contact, mainly e-mails to see how people were. Then my parents got quite sick at the same time & I was getting divorced too. All my friends had met my parents numerous times, they weren't faceless names to them,  but I didn't hear from anyone even once while all this was going on and they all knew about my circumstances.  All I wanted was an e-mail asking "How's it going?"  I didn't expect anything more than that.  So I did option #1 and let it fade. I jettisoned the works, quit bothering to contact anyone in my former city of residence and have heard nothing from anyone there since.  I'm slightly bitter as I considered these people very good friends but when it came down to it I guess I didn't mean much to them.  I wonder if they have even noticed my lack of contact? Out of sight out of mind? No one's so busy they can't take a minute to send a short email asking how things are.

 

 

that some feel if they don't 'need' you for anything then they might as well forget about you.

Who wants "friends" with attitude like that then. It's just that I valued the friendships & had been supportive to them when they had events like losing parents, illnesses, etc. Oh well. C'est la vie.  People come & go in one's life.