Tia Smith clutched her new phone in one hand and a phone case in the other as she shopped at a Best Buy in West Hollywood.

She clicked away into her smartphone's tiny screen and searched for the case in other nearby stores.

"I'm trying to buy this Otter phone case for my new phone," she said. "But I'm trying to see if Target or Walmart has it for cheaper so they can honor the price match," she said, as she scrolled through Target's mobile site on her new phone.

As more people turn to their smartphones and tablets when they're thinking about making a purchase, retailers and marketing companies are rushing to figure out ways to transform these mobile browsers into buyers. Some are providing special bargains. A few are tracking shoppers' every move around the store and nudging them to seal the deal.

During the fourth quarter of last year, mobile devices were responsible for 16.6 percent of online sales, up from 11.4 percent in the fourth quarter of 2012, according to an IBM study. Tablets drove 11.5 percent of those sales, compared with 5 percent from smartphones, IBM said.

"People are using smartphones and tablets on different occasions," said Charlie Anderson, chief executive of Shoptology, a marketing company. "They're using the tablet at night when they're on the couch or in bed and making purchases or doing research, and mobile is more for doing research while you're in brick-and-mortar stores."

Mobile shoppers are always on the lookout for a better deal, said Beth Craig, director of insight for Catapult, a marketing consulting company. In a study produced by Google last year, 44 percent of smartphone shoppers said they used mobile devices to shop because it saved them money.

Google's search engine is popular for comparison shopping, as are a proliferation of mobile apps that can read bar codes and other coded product identifiers using a properly equipped smartphone.

The field is still relatively young, so consumer product companies and retailers are still figuring out how to attract these mobile shoppers, said Adam Guy, senior vice president of business development for Millward Brown, a market research company.

Several retailers also have turned to special shopping apps. Some are fairly basic, guiding customers to various departments within a store, cluing shoppers in on specials and enabling shoppers to make shopping lists and load coupons electronically.

Tools that provide promotional offers and digital coupons tend to be among the most popular methods of marketing on these devices.

Walmart has released a more sophisticated mobile phone app that tracks a user's location using the phone's GPS and can offer in-store deals when it recognizes the shopper is in a store.

A few retailers are taking the concept even further.

In November, the Macy's department store chain began testing a product called ShopBeacon at stores in San Francisco's Union Square and New York's Herald Square.

The app, created by Shopkick of Redwood City, enables a merchant to offer discounts on specific products that a customer has expressed interest in or, perhaps, has lingered near, prodding him or her to buy.