With the popularity and ubiquity of Google, it has become a verb to describe "searching for something online" and it appears in conversations and informal writing.
How can I know if it is acceptable to use "google" in more formal writing?
It is now an official verb (since 2006), added to the merriam-webster dictionary and the OED.
So I would say: yes.
I generally recommend the following for using newly minted words:
Sometimes using "Googled" is appropriate for your voice in business writing. This will usually be in less-formal media like project-team blogs or webcasts (where the reader expects colloquial usage).
I think it's acceptable. This leads to some fun sentences, like "A few years back, I googled something on altavista and found ..."