using SearchMultiSelectCustomField

I am able to successfully search for a custom record based upon a specific value within a custom field of type string or text.  However, now I need to be able to search a custom field of type List/Record. 

Anyone know how I can include SearchMultiSelectCustomField into my code below ??

// ** code successfully finds field of type text **

public bool GetCustRecordBasedOnNsKey(string nsKey)
{
CustomRecordSearch crs = new CustomRecordSearch();
CustomRecordSearchBasic crsb = new CustomRecordSearchBasic();

crsb.customFieldList = new SearchCustomField[1];
crsb.customFieldList[0] = new SearchStringCustomField();

//((SearchStringCustomField)crsb.customFieldList[0]).internalId = "custrecord_tmw_prod_fam_comp";
((SearchStringCustomField)crsb.customFieldList[0]).internalId = "custrecord_tmw_prod_fam_acct_id";
((SearchStringCustomField)crsb.customFieldList[0]).