Hi,
Thank you for using Syncfusion products.
We regret to let you know that with the current implementation of code library the multi column drop down doesn't support shuch functionalities.
For search options i offer to use Auto complete textbox instead of multi column dropdown. Using templates we can use auto complete text box with multi column data.
http://samples.syncfusion.com/ASPNET/7.2.0.20/web/Tools.Web/samples/3.5/EditorsPackage/AutoComplete/TemplatedUserEmailList/cs/userchoicelist.aspxPlease check with the above online sample for the auto complete text box template support and let me know if you had any queries.
Regards,
Pradeep.