192.168.20.121

Please help, This guy is pretending to be a gal and making troubles with my family,. please help me. who is he?

You CANNOT trace that address as, by it's nature, it is untraceable.
That's how private addresses work.

Where did you come across it ?

And of course, if they are causing trouble, call the police.

If you know they are pretending to be someone, stop contact with them on the computer.

Best thing to do is to call the police.

I think I got it wrong,.

Someone is bothering me and my family but cn't find out who.., I tried to track down the ip address but I think I got it wrng,, Is der any way to find out ip address of a fb user or any info who that guy is?

No you will not know what someone IP is on Facebook.

You can turn it over to the police who can look up records if there is cause with a court order.

Or report it to Facebook as harassment.