Moved to Site Feedback & Help forum
Two easy ways to send a PM:
1 - click on the user's avatar somewhere on the forum. A little window will pop up with some information about them and there is a text link in that window to "start a conversation". Just click on that and his/her name will automatically be populated as the recipient on the message
2 - Mouse over "Inbox" at the top left of the page. A window will drop down with a link to "start a conversation" that you can click. If you go this route you'll have to manually enter the name of the recipient