“Miss you” is the present simple form of the verb to miss and “Missed you” is the past simple form of the same verb.
The verb “to miss” has a few different meanings so let’s understand when you need to use “miss you” or “missed you” depending on the context.
“Miss you” is most commonly used when you feel that you are lonely without a person. You want them to be in your company again because you have a strong connection with them.
I miss you, John, I haven’t seen you in ages.
It seems like ages since we last spoke! I miss you!
“Missed you” is more common in the context of when you tried to meet someone but they weren’t there.
Imagine that you want to meet your boss but he has gone out for coffee. You could send him an email saying “sorry I missed you earlier”.
What is the difference?
“Miss you” is a feeling that you usually have in the present tense but there can also be a situation when you meet the person again and you can say “I missed you”