I had a dig through the code, and a number of things indicate that twitter's search methods are not supported. For instance, the base_url is https://twitter.com, whereas the search API says that it's necessary to use search.twitter.com:
The Search API doesn't require authentication so I haven't worked in any support for it yet. You can just make straight up calls to the API like this:
That's a simple example, but it works. I will be adding Twitter Search support as an eventual result of #1 because I will be integrating search into my TwitterDispatch gem. Hope that helps.
This will be implemented once Grackle is integrated into TwitterAuth.