Can you tell me about Facebook friend features?

[Person]

I've noticed that people I used to be "friends" with on Facebook sometimes can no longer be found. I will do a search for them and they won't come up. Why is this? Have they "unfriended" me so I can't see them anymore? If I "unfriend" someone, will they get a message or do I just disappear in their "friend" list and they can't search for me either?

Also, how does the "newsfeed" feature work? Does it just pick random comments from friends and post them in no particular order? If so, does this mean everyone sees different random comments on their "newsfeeds"?

[Michaela]

They either deleted and blocked you or deleted their account. When you delete someone the don't find out about unless they are really freaking observant. Anything that your friends post on facebook gets posted in your newsfeed.

[Jenna]

If you can no longer see someone in your friends list, it means they deleted you. That's how it works: the other person doesnt get notified of this. If you can't even find them when you search, they may have deleted their account altogether.
The Newsfeed is a compilation of things that your friends have been up to, but it's not entirely random. Facebook will select content from friends who you commonly view, chat with, or comment on. You can manually adjust this by picking which friends you are "subscribed" to, by pressing the button at the top of their profile page.