"I'm missing someone" vs "I miss someone"

I'm missing someone, this sentence is correct? and what is the difference it then I miss someone?

Tense of both the sentences are different, hence both of them convey a completely different meaning. Let's tackle both of them:

1.

"I'm missing someone" This sentence is in present continuous tense therefore here it means that you're missing someone at that particular moment. This sentence is generally used when you're having a conversation, so as to show your present state.

2.

"I miss someone" This sentence means you you miss someone often. It may also mean that you are missing someone at a particular moment while not necessarily. This sentence here can take both the forms depending on the condition hence it is a conditional - sentence.

I hope I was able to make it clear to you. Please leave a comment in case you still have a doubt.