Online sales jump on Cyber Monday, eBay shines SAN FRANCISCO (Reuters) - Cyber Monday's online sales got off to a brisk start, sending e-commerce retailers' shares higher and suggesting strong growth from earlier in the holiday shopping season would continue through December. Sales on eBay Inc's online marketplace were particularly strong and Amazon.com Inc continued its rapid holiday shopping season growth, according to early Cyber Monday data released by e-commerce firm ChannelAdvisor. EBay's shares climbed about 5 percent to $51.50, a new multi-year high, in afternoon trading. Amazon's shares gained 1 percent to $242.26. Cyber Monday has been the biggest online shopping day in recent years, as workers return to offices and use computers to make holiday purchases. ComScore expects online sales to hit a record of about $1.5 billion by day's end. Online sales rose 24.1 percent as of noon EST on Monday, compared with the same period a year ago, according to International Business Machines Corp, which tracks transaction data from 500 U.S. retail websites. In 2011, the early Cyber Monday year-over-year growth was 15 percent, IBM said. Strong online sales growth on Thanksgiving Day and "Black Friday" sparked concern that shoppers were just buying earlier, threatening revenue later in the season. "So far that is not the case," said Jay Henderson, the strategy director for IBM Smarter Commerce. Extending the shopping season has really just fueled additional online spending rather than cannibalizing days later in the season. ChannelAdvisor said client sales - or sales generated by third-party merchants using the company's software and services - soared 57 percent on eBay.com early on Monday, compared with the same period in 2011. The sales growth rate was five times higher than during the same period last year, said ChannelAdvisor, which helps merchants sell more online. "The early eBay numbers are impressive," said R.J. Hottovy, an equity analyst at Morningstar. They put together an effective marketing plan across several channels this holiday season - online, television and print. EBay has been trying to move away from its online auction roots, emphasizing new items selling at fixed prices to better compete with Amazon. "The numbers suggest they're having success reintroducing consumers to the 'new eBay,'" Hottovy said. Client sales on Amazon.com were up 52 percent during the first part of Cyber Monday, ChannelAdvisor also reported. "Amazon continues to look impressive to us since it is building on top large numbers," said Scott Tilghman, an analyst at Caris & Company. Reporting By Alistair Barr; Editing by Maureen Bavdek