Shares of eBay (NASDAQ:EBAY) jumped as much as 12.5% in after-hours trading, as investors reacted to the e-commerce specialist's fourth-quarter results.

Revenue for the quarter increased 13% year over year to $4.5 billion, driving a 15% increase in adjusted earnings per share. Both figures were in line with analyst estimates.

Forty percent of the 36 million new eBay users in 2013 use mobile apps on the trading platform, an 88% annual increase. More than half of eBay's enabled commerce volume, or ECV, was done on mobile devices.

The PayPal electronic payments system handled $52 billion of customer payments in the fourth quarter, and $180 billion over the 2013 fiscal year. In a testament to PayPal's reach outside eBay's proprietary systems, PayPal transactions are growing at a 25% annual clip -- faster than the 22% growth in eBay's own trading and storefront properties.

Separate from the earnings report, activist investor Carl Icahn announced two nominees for eBay's board of directors earlier today. Wielding a 0.8% interest of eBay shares, Icahn wants eBay to spin off PayPal as a standalone business. Current leadership disagrees, citing synergies between PayPal and eBay systems and markets.

"PayPal and eBay together create an incredibly strong global commerce ecosystem for consumers and merchants, and we continue to see tremendous growth opportunities ahead," said eBay CEO John Donahoe in a prepared statement.