Hmmm....well are you actually chatting with the person? If so, there are a couple ways to do it.
If so, there's a couple of ways to go about it.
he first way to do it is to open your command prompt. This is what you'll be using to find the person.
while your chatting with him, send him something, anything. Send him a file, a picture, anything. If you think the person might be sketchy about it, use your imagination and be creative.
While the file is transferring, type in the command line: netstat -n .
Be sure to note the space between "netstat" and "-a".
While the file is being transferred, you are making a connection to your computer. that means that the i.p. is connected to you, therefore letting you transfer the files.
However, a person's ip can change depending on where they are or where they are connected.
Yet assuming that this isn't the case, we can glean a little information here.
Using this method, we of course fine out the I.P. address after a little information sorting. At the same time, we might even possible find the MAC adress as well.
Both of these are pretty much useless to us.
However, you can go to this website:
http://www.lost-computer.com/cgi-bin/cgiwrap/absolute/WHO.CGI
this will give you the infomation about what router they're using and who's providing their internet, and a few more details. If you contact these providers with the information displayed and give them your story, or if you talk to local authorities, you will most likely be helped.
Also, I'd say look around at softwares maybe. There are tons of hacking softwares everywhere, and a lot of them are extremely effective. I've used many softwares myself recreationally, and it's surprising just how much information you can get from a good hacking device. If you have any other questions, feel free to email me at "thelorddragonreborn@yahoo.com"
I don't have all the answers, but I can certainly try to help. lol, it gives me an oportunity to learn more, if anything. Hope everything works out for you! =)