Legal advice - Harassment from overseas.

Hi everyone. I'm going to try make this as simple as possible.

For the past 6 years, an ex online friend has been on and off harassing me and the people around me. He has also doxxed both me and my friends, as in exact home addresses.

This person lives in the United States. I am from South Africa. Is there at all any way to go about this legally? I know it'll be difficult to do much as it's almost anonymous profiles, but I thought I might as well ask. I think I know a bit about this person's personal details, and I could most likely identify them if I was to be shown a picture.

This person knows exactly where me and my friends live, and quite frankly I am terrified.

Is there anything legally I can do to prevent them from coming in contact with me again? Their main goal is to ruin my life. I cannot deal with it anymore.

Please help me out. I'm lost on what to do. Is it worth seeking out a lawyer or something?