Yes, of course you can! I’d be delighted.
But when I have been asked to create a postcard group on Facebook I have declined. I do not need another thing to keep track of in my life. Share your postcards in the mixed media and mail art groups you’re already in, or on your own Facebook wall.
If your profile is open I will be notified and see your cards if you write something like: “A postcard made for the DIY Postcard Swap of Studio iHanna” where Facebook will link Studio iHanna to my FB-page. This does currently only work if you have liked my FB-page and are on the Facebook site from a regular computer, not an phone or ipad app!
Also tag your post #ihannaspostcardswap – because tags work on Facebook too and are rather useful.