Sentences with form "are being " + past tense
are they correct form of grammar. And what tense do they represent.
You are being missed.
Yes, it is a grammatically correct sentence in the Present Progressive tense. It uses the Passive Voice too.
It says that someone is actively missing you (wishes you were near them), but says nothing about who exactly is missing you.
Transforming it into the Active Voice, we may get the following sentence:
[We are] missing you.
What can vary is the part in the brackets: it depends on who exactly is missing the person. It can me [I am], [she is], [he is], [they are] etc.
The word missed is not in the Past Tense in your example. It is in the Past Participle form. It has been put into this form to help form the Passive Voice construction, which consists of the verb to be + Past Participle.
Your sentence without the Progressive aspect will look like this:
You are missed. (BE + Past Participle = Passive Voice)
Then we add being to form the Progressive Aspect, in order to highlight the fact that the process of missing you is actively happening right now, that someone is actively missing you at this moment:
You are being missed. (Passive Voice + being to form the Progressive Aspect)