1) Dotdotcircle finds your most recent IP address.
2) He either IP pinpoints to your address or hacks your VoIP modem to get your phone number (if it's possible, and if you even have one). This process can be sped up with data-mining for your personal traits and social networking. A simple pinpointing of your birthday within the radius of where you live can make this process faster.
3) He then looks up your address to find the resident(s).
4) He then looks in your country's census for your relative information.