Last week was a strong one on the market as the Dow Jones Industrial Average (DJINDICES:^DJI) gained 3.3% and the S&P 500 (SNPINDEX:^GSPC) rose 3.6%. Hope for avoiding the fiscal cliff and some strong readings about housing helped drive stocks higher, but this week there will be a big focus on retail stocks. The holiday shopping season has begun, and investors will be taking a close look at retail stocks that may be winners or losers over the holidays.

According to comScore, Black Friday's online sales rose 22% to more than $1 billion. The data company expects holiday online retail spending to rise 17% this year to $43.4 billion. That's great news for online retailers such as Amazon.com (NASDAQ:AMZN) and eBay (NASDAQ:EBAY), which will be in focus this week.

One interesting development is that people are spending more time shopping online from tablets this year. IBM's (NYSE:IBM) Digital Analytics Benchmark showed that 24% of online shopping came from a mobile device and Apple's (NASDAQ:AAPL) iPad generated  10% of all online shopping by itself. The tablet accounted for 88.3% of all tablet traffic, according to the report, showing just how dominant the tablet is.

Physical-store sales were a little less impressive. ShopperTrak said Black Friday sales were down 1.8%, but some of those sales may have slipped into stores that opened on Thanksgiving. Overall foot traffic did rise 3.5%, so at least shoppers are out and about.

The trends aren't good for struggling retailers such as Best Buy (NYSE:BBY) and J.C. Penney (OTC:JCPN.Q), which aren't nearly as strong online and needed better bricks-and-mortar sales. These stocks may come under more pressure as they continue with their turnaround plans.

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