If you want to say "I Miss You" in the Tamil language you would say the following:
Naan unnakalai miss
Naan means "I", unnakalai means "you" and miss comes at the end of the sentence in the Tamil language.
You can also say:
Naan unnai miss pandren
This is a more informal way of telling someone you miss them in Tamil and could be said to a friend or partner.
If you want to tell a friend that you missed them in Tamil, then you could say the following:
Nanba unnai rombha izzatu vitean
This literally means "I miss you so much my friend", and is quite an informal and friendly way of telling your friend that you missed them.
Another phrase which has a similar meaning to "I miss you", which you may want to use on your loved one is:
Naan unnai engagirean
This means 'I am longing for you' and is often said to someone who you are in a relationship with - such as your husband, wife, boyfriend or girlfriend.
I hope you find these phrases helpful in expressing how much you miss someone in the Tamil language :)