The website acts as a directory and message board so people can look for lost loved ones or post a note saying they are safe.
It is designed to be embedded on websites and social network pages to reach as wide an audience as possible.
The system has proved useful after other disasters that have stopped people getting in direct touch.
The extent of the damage caused by the Japanese earthquake is not yet known but its magnitude and the widespread devastation wrought by the subsequent tsunami is likely to see tens of thousands displaced.
Before the advent of tools such as Person Finder it was much harder to compare the information gathered by separate agencies and help to re-unite families and friends.
Underlying the site is a common format for describing people who are lost or who want to announce they are safe by whatever means they can.
In the wake of disasters, many volunteers in other countries often scrape sites for this formatted information and add it to the People Finder database. Others take information from blogs, texts and tweets and convert it to the format so it can be put in the database.