Shares of Google, the No. 1 search engine, swooned nearly 8 percent Thursday after the company reported a fourth-quarter revenue miss while earning less than expected.

Google shares fell to $591.33, down more than $48 after hours, after the Mountain View, Calif.-based company reported lower-than-expected results.

The slide lopped more than $12.3 billion off Google's market capitalization.

Google reported fourth-quarter net income of $2.71 billion, or $8.22 a share, up from $2.54 million or $7.81 a share in 2010. But analysts had expected earnings above $9.03 on a net basis and $10.51 a share on an operating basis.

As well, revenue came in at $8.1 billion, about $300 million shy of analyst estimates. Still, there were promising signs: signups for Google+, the social network that competes against Facebook, now exceed 90 million, or about 10 percent of Facebook members. The signups came over only six months.

Google, which plans to close its all-cash $12.5 billion acquisition of Motorola Mobility this quarter, reported cash and investments of $44.6 billion, about $2 billion above the third quarter.

CEO Larry Page was scheduled to brief investors Thursday night. By tradition, Google doesn't issue earnings forecasts unlike Intel and IBM, which also reported results late Thursday.