Go to "Community" between "Calender" and "Forum Actions" the list will drop down and at the bottom of the 4 choices is "Member List"
Or you can scroll all the way down to the bottom of the main form page and see if the person you are looking for is "on line" with all the other people, if they are just click on their name and if your "logged in" it should take you right to where you can send them a message.
It's there, Bob. Just a different way to get to it:
Find the "search forum" from within a forum, or "search thread" from within a thread. Select "advanced search" and when that page opens, click the other tab "search multiple content types" then check the "posts" box and search by username. Not as bad as it sounds...