That doesn't do it for me. It just gives me my Buddy List and that doesn't seem to work anymore. E.g., I was Messaging with a pal who is on that Buddy List and his entry there never lit up: no green camera.
He explained the way to do a Share My Desktop/Screen sharing was to type the name of the person whose screen you want to share into the Messages To: box, then, when contact is established, click on the camera icon next to that To: box.
Worked just fine.
How do you get the old Buddy List to "light up" showing the person with whom you are exchanging Messages?