Yep, a post rebake from the console will do it: Rebake all posts? - #2 by zogstrip
But before you do that make sure this is big:
Otherwise those posts won’t have their remote images brought into the forum and the thumbnails won’t then be created.
The Theme Component is work in progress and you need the ‘plugin sidecar’ installed for the complete feature set. Actions is not yet supported but will be soon when I get a moment.
Oh, how so? There is a slight approximation made on tile size, but apart from missing actions it should be identical (aside from the tiles ships with slight drop shadows on the TC which I prefer personally).