There are also sites that cater specifically to dating and marriage. These sites are primarily accessed by mobile phone and visitors are able to communicate directly with each other. The murders have occured in locations all over Japan and some have involved people from opposite ends of the country. In the real world there is enough of a foreign population in Japan these days for just about every sport or common hobby to be accessible in English. There are clubs for things as diverse as softball rugby, martial arts dojos, flower arrangement, amateur radio, swing dance and foot fetishists.
Most countries have their own society or network, many of which are online, too.
There's just too much for me to try and list them all here and keep them updated. Your best bet is to check the classified magazines below. Some clubs as well as the magazines themselves organize regular parties. And of course there is always good old daily life. Japanese people, in the cities anyway, have become much more used to seeing foreigners.