Last week was a strong one on the market as the Dow Jones Industrial Average (^DJI 0.40%) gained 3.3% and the S&P 500 (^GSPC 1.02%) 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 (AMZN 3.43%) and eBay (EBAY 1.32%), 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 (IBM -1.05%) Digital Analytics Benchmark showed that 24% of online shopping came from a mobile device and Apple's (AAPL -0.35%) 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 (BBY -0.25%) and J.C. Penney (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.