Go to inbox. Go to start new conversations and put the persons name that you're looking for or the user ID and that should help start the conversation and private messages to that person.
1) New members need to make one post before the private message system is made available.
2) You can always access your conversations with this link while logged in: http://tokyoadultguide.com/conversations/ -- (after the first post is made and the system updates your account automatically)