The Search Panel can find text only from visible grid columns. So, it is necessary to create a column with a field that contains a PreviewRow. It is possible to hide it using the CSS styles:
[ASPx]<dx:GridViewDataTextColumnFieldName="Description"VisibleIndex="2"><HeaderStyleCssClass="hiddenColumn"/><EditCellStyleCssClass="hiddenColumn"/><CellStyleCssClass="hiddenColumn"/><FilterCellStyleCssClass="hiddenColumn"/><FooterCellStyleCssClass="hiddenColumn"/><GroupFooterCellStyleCssClass="hiddenColumn"/></dx:GridViewDataTextColumn>
[CSS].hiddenColumn{display:none;}
Then, it is necessary to highlight the found text manually in the same manner as performed in the ASPxGridView - Search Panel - How to highlight the text placed inside a DataItem template example.