You may want to start here: Google’s Person Finder. [NB: Google rolls one of these out for every major disaster where people go missing and communication is difficult.]
My heart and thoughts are with the people in Japan, everyone throughout the Pacific region who are experiencing ramifications of this natural disaster, and anyone whose loved ones are in the affected areas.
For more information:
Shakesville’s run down (a really great source for other sources, as well as an on-going thread/discussion).