"ฉันกำลังคิดถึงคุณอยู่"

แปลว่า: I am thinking of you.

[wanderdugg]

Is "I'm thinking about you." not also a possible translation?

[thana292594]

จริงหรือ 555

[ApionNamwi]

I missing you

[T1mmy99]

Good, almost right. But, in English when you use verb 'ing', you need the right form of verb 'to be' as well.
So here, 'I am missing you' or 'I'm missing you' would be fine'