Google only really does http/https, finding mongodb requires scanning for 27019 and then pointing a client at it.
I believe Shodan does this.
..including any private data they can gather on you, via search, maps, analytics, browser..
I wouldn't put it past Google to be already indexing exposed databases (or continue indexing ftp), just not making it publicly available.
Between MongoDB, Jenkins and Elasticsearch, thats a whole ecosystem of pwnability that is probably just starting to be exploited.