* Fourth-quarter revenue beats Wall Street targets
* Mobile ads represent 53 percent of total ad revenue
* Shares up 10 pct in extended trading (Adds comments by chief operating officer, updates after-hours stock price)
SAN FRANCISCO, Jan 29 (Reuters) - Facebook Inc's fourth-quarter revenue jumped 63 percent, beating Wall Street targets, as the Internet company's mobile ad sales continued to accelerate.
Shares of Facebook surged 10 percent to $58.90 in after-hours trading on Wednesday.
"The mobile shift is happening and it's working really well for Facebook," Chief Operating Officer Sheryl Sandberg told Reuters in an interview.
Facebook said it now has 1.23 billion monthly users, with 945 million accessing the service on a smartphone or tablet.
The world's largest social networking company said that revenue from mobile ads represented 53 percent of its total advertising revenue in the last three months of the year, or $1.24 billion, versus the 49 percent proportion that mobile ads represented in the third quarter.
Sandberg credited the strong fourth quarter revenue growth to increasing demand by marketers for mobile ads, Facebook's improved tools to demonstrate the effectiveness of its ads and a growing number of small businesses using Facebook.
She said there are roughly 25 million small businesses worldwide that have created free Web pages on its social network. She did not provide an update on how many of those were paying advertisers, though Facebook has previously said that it counts more than 1 million small business advertisers.
Overall revenue in the fourth quarter rose to $2.585 billion, compared with $1.585 billion in the year-ago period and above the $2.33 billion expected by analysts polled by Thomson Reuters I/B/E/S.
Facebook reported net income of $523 million, or 20 cents a share, versus $64 million or 3 cents a share in the year-ago period. Excluding certain items, Facebook said it earned 31 cents a share. (Editing by Matthew Lewis)