If Google+ looks like a ghost town to you, Vic Gundotra, Google’s svp of engineering, thinks the problem isn’t his social service, but you.

During a one on one conversation at the South by Southwest Interactive conference, blogger Guy Kawasaki asked Gundotra about recent criticism that Google+ isn’t getting much traction.

His response: “Make sure you’re using it correctly.” (Sounds a bit like Steve Jobs during antennagate, no?)

The majority of content is shared privately to circles, Gundotra said, adding that if you visit a page and it looks empty, “Maybe they’re just not into you yet.”

The industry may have the impression that Google+ is languishing, but Gundotra said it's the fastest-growing service Google has ever released and now gets 100 million active users over a 30-day period.

Gundotra also took a subtle dig at Facebook’s approach to advertising.

“We think we should not be injecting ads

Instead of surfacing ads while people are looking at family photos or pics from a best friend’s party, he continued, Google’s approach “marries the best of social with the best of commercial intent.”

That means ads won’t appear on Google+ but when people are searching and, through Google’s social search features, see that a friend has +1’d a business or restaurant.

And, he added, early Google data now shows that socially-annotated ads (those that have been +1’d) get a 5 to 10 percent uplift in click-through rates.

“That allows us to not jam ads into photos of your daughter,” he said. “It’s serving the ads when they’re relevant.”