Thanks in advance,
I would recommend the Linefilter2 plugin. I use this alot to extract search results from very large log files. As for doing it with multiple files, I don't think the plugin can do that.
If you know Python pretty well, you could use the Python Script plugin (available in the Plugin Manager) to put together something that will go through multiple files and do the same thing, however I don't know the API well enough to accomplish that.