Wall Street investment bank Stifel Nicolaus just downgraded Google from a buy to a hold, saying the Internet’s center of gravity is shifting from Google to Facebook.

The bank is worried that growth in Google’s core business may be slowing due to the onslaught of mobile and social media websites like Facebook.

With more than 30 percent of Internet minutes spent on Facebook the Internet’s center of gravity is shifting from Google to Facebook, analyst Jordan Rohan said in a note to clients.

“Search just isn’t the bright shiny object that it was when Google became a public company in 2004,” he wrote.

As social and mobile media emerges, there is reduced advertiser enthusiasm to spend more on Google, Rohan added.

“Large acquisitions like Motorola Mobility may become more frequent and could distract Google’s senior management team,” the analyst wrote.

In August Google said it would buy Motorola Mobility Holdings for $12.5 billion — its biggest deal ever — and sparked investor concerns that the deal would take Google deeper into the competitive hardware business and threaten its popular Android operating system.