Try to use RadAutoCompleteBox to achieve your scenario. Telerik RadAutoCompleteBox for ASP.NET AJAX is a powerful drop-down list control which gives the ability to select multiple entries, displaying them as a sequence of strings separated by a delimiter, or fancy styled tokens depending on your preferences. Please have a look into this help documentation and online demo for further help.
Nice control but the limitation is that the token values must be from the list. I found only server-side example how can I do it http://demos.telerik.com/aspnet-ajax/autocompletebox/examples/programming/addremove/defaultcs.aspx.
Is there any way to achieve it client-side? In fact, I have no list to match, I just need to tokenize entered values.