Recent reports have indicated that Google+ has struggled to keep brands engaging. It's not exactly the first place fans think of for engaging with celebrities either typically (unless perhaps they're trying to engage with Wil Wheaton or look at photos of Hugh Jackman).
Some celebrities just rehash the stuff they're sharing on Facebook or Twitter. That doesn't go for Rose McGowan. I think it's safe to say she's an active Google+ user - one of the 390 million Google boasted this week as it launched a slew of new features.
If you want to see McGowan showing off her "fish face," you're going to have an easier time finding it on Google+ than you are on Facebook or Twitter.
The Eternal Fish Face
Afternoon fish face #naptime
Party (and fish) face