"concerned with" means involved with or connected to "concerned about" "concerned at" and "concerned by" all mean worried about So correct usage would just depend upon the intended meaning. the rest are incorrect usages :) WHY ? Because English is made this way :) Other ways to use : My concern FOR you is endless

If you are worried about someone then 'concerned about you' is correct.

concerned about and concerned for are both correct, 'I am concerned for you' means your worried about the person's own welfare 'I am concerned about you' (also 'I am concerned by you') can mean that you're worried that they could pose a threat to you or others. Compare 'I am concerned about/by global warming' and 'I'm concerned for the environment'.

i am concerned about you

I am concerned about you.