you cannot use tracert to find out someones IP if they are using proxies.

in order to use tracert you need to know an IP already. If you do know it, and they are using a proxy, all you will know is the ip and, the route your tracert takes back to the proxy. Sure, it can give you some interesting information, but the only way(that I know) to trace someone through multiple proxies is to have a look at the log files at each of the proxies.