Checkout the online demo which demonstrates how to use client-side filtering for RadComboBox, which is similar to the google filtering. ComboBox / Filtering
To enable the filtering mechanism of the combobox you need to set the Filter property to either Contains or StartsWith
Another option is using the client-side Autocomplete for the radcombobox. To enable this behavior you must set the MarkFirstMatch property
to true. Demo - Autocomplete