"Andar" in place of "estar"

I've noticed that in some contexts, people replace estar with andar. I was curious if anybody could explain when this is okay/not okay to do, and if it is considered informal?

Examples I think work:

Anoche salimos a una gran fiesta. Por eso todos andamos crudos hoy.

Andaba enfermo – por eso no fui al cine con ella.

¡Hola! ¿Cómo andas?

Examples I'm not sure about:

Ando extrañándote.

Thanks for any help!

submitted by /u/thepeoplestarttomove
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