There are no online White Pages for people in Japan at this time - this is because they value their privacy and also very few people are listed in the paper version. If you know the address of the person and they are listed you may be able to get help from the directory enquiries on 104 from inside Japan.
Country code: +81
Really good English version of TownPage Business and Services telephone directory from Nippon Telegraph and Telephone (NTT) with an easy to use search function. Search options include distance from individual metro stations and results include information on whether or not places have English speaking staff and opening hours. An excellent directory for anyone visiting or living in Japan.
Business Directory for Japan. In Japanese. Search by keyword (キーワード検索) or location/objective (場所×目的検索) then press the blue search key beside the input box.
Business directory covering over 11 million across the country, searchable by keyword, region and industry. In Japanese. Shows maps and travel info with results.
Basic business directory for Japan - search by keyword or category.
Business directory for Japanese related companies in the USA. Also includes reverse search and zip code search.