Nintendo of America has shared that North American Splatoon players can now access SplatNet to check the playing status of their friends through the online interface.
SplatNet was already released in Japan, where JP players have been able to know when their friends were available to play. Be sure to login to the site with your NNID, and see who is playing. The site also allows users to link their Twitter accounts to the SplatNet. This would obviously allow others to know when players begin their Splatoon play.
As always, gaming is meant to be fun, so keep gaming!!