Hi Flavio,
I am afraid Group Titles have not been implemented yet in RadTileList for ASP.NET AJAX. You can find the request here: http://feedback.telerik.com/Project/108/Feedback/Details/124614-add-title-for-the-tilegroup. The page allows you to cast your vote to increase the item's priority, leave a commend and/or follow the idea's progress.
Regards,
Telerik
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