TRichView.com

to search for a simple text string in a bunch of .RVF files?

Is there a specialized function for this or do I have to load each RVF file in a TRichView and search the text in it?

You need to load files in TRichView (or TRVReportHelper.RichView).
However, I do not recommend using SearchText, because this procedure selects the result, and selection requires formatted document. Formatting is the slowest procedure, so it should be avoided unless it is necessary.
Instead, enumerate document item by item and search a substring in text items.