"Мне пофиг" is used more friquently now than "Мне плевать".
Sometimes you can use "меня это не волнует" if you are speaking about an object but not about man.

I miss you – я скучаю по тебе.
I don’t care – я не беспокоюсь, but they say usually «Мне всё равно» (literally – all is the same). «Мне плевать» и «мне пофиг»- are rather spread amongst the young people but impolite.

Мне без разницы - also very good and often variant for "i don't care"
Я не беспокоюсь - rare and only as a transitive verb!
an example: Я не беспокоюсь о том, что с тобой случится.
there are also lots of dirty language variants im not sure i should and can bring them here..