Hi,
Given that Selectize is just another jQuery-based custom control (http://selectize.github.io/selectize.js/), the answer is : yes, it can be controlled with TestComplete.
See also amazing description by Lino about custom web controls: https://community.smartbear.com/t5/TestComplete-Functional-Web/TestComplete-9-3-Does-it-support-kendoUI/m-p/81168#M17730
The opposite side of all fancy stuff done using jscript in Selectize is that you will have to manually investigate control on TestComplete's Object Browser to learn how to expand and collapse it, how to select the value and how to get the currently selected value. This is the price you must pay for the decision to use non-standard customized stuff.
