Once upon a time, you could hover your mouse over someone's profile picture and a little pop-up would appear with a Send Message option
And, to be honest - that options still appears.
IT JUST DOESN'T WORK
If I select Send Message, all that happens is that I get taken to my Inbox with the Search function activated, although the page says "Compose New Message".
What I EXPECTED to happen (and USED to happen) is that the Create New Message (to the user you had selected to Send Medsage to) already in the recipient list. Like this: