Hi my question is if I follow someone on a social network an then he sends me a message asking me for illegal stuff,will I be implied in the future when he get caught because of his illegal activities ,just because ia add him first as a friend?I unfollow him and already deleted my account on that website ,I'm really worried

You can be implied (depending on where you and the other person is located)
You would have to produce clear evidence that you told them no, and that you never discussed doing it.

It would be best if you showed that you reported this to the authories.

I didn't send him any message I just add him

So after knowing of his desire for criminal activity, you did not tell you no, and you did not report him.
Did you ban him ?

If the police came to your house to question you, what could you tell them, on how you made sure he understand you are not part ?

If he did it, and you knew about it, and did not report it, you also can be held liable.

You could be implicated as well as any other contact of this person, but as Fr. Chuck has said the best defense against being implicated in his illegal stuff is to report him to the proper authority.

I disagree with all above.
No, you are not implicated, nor are you at fault for not responding to his request.
You don't even have to report him.