Facebook and twitter, i checked your facebook page i dont know is it offical or not but it just pusblish blog entries. i know your current users love blog and planet but everyone else have no idea about linux or mint or blogs.
you really have to add some stuff on your facebook and twitter page, instead of just using those pages for publishing your blog entries. everyone has a facebook account and it can be used for free commercials. facebook is very effective and very important. Also you can use new popular websites like 9gag to make some viral campaings. you can do some commercials like:
write your name suggestion about x tool here and we will make it! ext.
best wallpaper of the month.
best application for picture editing.
Inform your users with mailings. If someone left using mint they can remember you via mail.
Web Site Change:
Change your website. When i entered your webpage. I have no idea about linux or mint. I just see some random info what is KDE, what is RC? (i know them giving example dont worry for me )
Ubuntu's web page is good example for this. Look at this page http://www.ubuntu.com/ubuntu its very very good example. If you dont have web designers well ask to your community!
Create a marketing team:
Developers cant do marketing. You have no time for this. You need designers, text writers, art directors ext. Find a marketing director and let him lead this kind of stuff.
Let your local communities arrange meetings with their community. People would like to see each other. They can share their ideas and can find good ideas for supporting you. You can have a facebook page your international but your local communites can share your ideas with their own language. You can prepare a document for those people. Teach them what they have to do.