If you are looking for trouble, you found it.
If you are looking for trouble, you've found it.
the second one(past simple seems strange here)means that the troubles are still there not the first one. I think the second one is better because "if you are looking for trouble" implies present or future so present perfect should fit better. What do you think about it?
They are equally correct.
Simple past is grammatically correct and conveys the intended meaning. You can use either simple or perfect in this case. I can't see a reason to prefer one over the other.
In your sentences the speaker means the speaker is the trouble, and the person being spoken to has just now--in the immediate past--found them. Grammatically, nothing about the future is referenced. Semantically, the threat of trouble will play out in the future, but that's not part of the grammatical structure of these sentences.
If you want a future tense version, it would be: If you are looking for trouble you will find it. And it will be me.
The past and past perfect give a more immediate feel and convey the 'it' through context. The future tense would be more appropriate if spoken by someone who is making a threat for a future encounter.
Present tense doesn't work: If you are looking for trouble you are finding it.
That's grammatically correct but not idiomatic and sounds like a non-native speaker.
The comma is not necessary and could be replaced with a semicolon or a space.
