Use the program-sniffer, if you want to know the IP address of the person with whom you have a connection. A sniffer is a small program that tracks the routes along which passed traffic and is part of the picture the path was information. It contains the addresses of destination points, as a rule, the sender of the network packet (roughly speaking, of a piece of data) and the recipient. Accordingly, the recipient is the one whose IP address you want to calculate. For this you will need to have a relationship with the user and try to give him any details (or get them from him), everything else will take the program-sniffer: from data packets transmitted over the network, learns the route and determine the address of the recipient/sender and displays them. Also, if the user is in local network or behind a proxy server, advanced sniffers allow you to circumvent even those restrictions that impede the calculation of an IP address.
Try also specialized ways to know IP address by exploiting common software, such as Skype, ICQ or by tracking. Such options are published on news sites or forums where practiced search and detection of these vulnerabilities. If one uses software that has a vulnerability, then it can be used in order to calculate the IP address of the source. However, it is worth mentioning that such activity is a criminal offense, if you do not take measures to hide private network addresses.
Please contact the site owner where man is, IP which is trying to find out. The organization has this data. If you can justify why you need that data, you can go to a meeting. Usually this information is not disclosed, but there are exceptions.
Find out your IP on the specialized websites, for example http://2ip.ru/. Data will be provided immediately after your visit resource. If you open the site number will be listed on the page.