SITE FIND/SEARCH <file *keyword*>

[FTPServerTools]

Or use my site search http://tinyurl.com/freeftpservertools/files which works on command line..

ioFTPD setup:
edit ioFTPD.ini and add under [FTP_CustomCommands]
SEARCH = %EXEC ..\scripts\sitesearch.exe TIMEOUT=5000 START="%[$path]"

ioFTPD and ftp client side effects:
if the query takes too long your client will return without a result. To avoid that use the TIMEOUT=.
etc.. just read the text file..