Recursive search is the default. You should just be able to do the following without specifying a folder wildcard:
bw list items --search google
If your search is not returning the items you expect, there could be another issue at play. For example, make sure you are using the latest version of the CLI (currently = 1.21.1).
EDIT: I just updated to the latest version after posting this, and now the CLI is no longer recursively searching through the folder tree. So I am guessing this must be a bug. Maybe @tgreer is able to comment if the search behaviour has changed or there is an issue with the latest release?