I'm trying to figure out how to embed the private message

I'm trying to figure out how to embed the private message button into the sidebar of a listing page I have: http://4bc.907.myftpupload.com/listing/adam-mann/

I couldn't find the widget to do this.

I also tried putting the shortcode "[pm_user]" into a new page, just to test it. But it still didn't work.

Can you please help me figure this out by posting clear instructions on how to do the shortcode? Thanks