That's right...you can only click on "your buddy" names if they are online. -- however, you can click where it says "buddy list" and it will bring up a page that lists everyone on your list. You could then copy a name from there and paste it into a PM.
OR....
Sometimes I don't get the spelling right & then the message doesn't go through.
When you start typing in a name in the PM, you should see a drop down list of names of those registered members of FC who has a username that matches the letters that you are typing. You can scroll down that list and then click on the name that you're looking for and it will add that name to the PM--For ex: If you click on "ajr" ...a list of all members who username starts with these letters will appear. If you scroll down until you find "ajrsmom" and then click on my name, it will automatically add it to the PM so you dont have to worry about misspelling the username.
Does this help to answer any of your questions? If not, let me know.
