Facebook’s billion-dollar purchase of Instagram made a lot of noise — so much noise that few people noticed when the company snapped up two more start-ups just a few days later.

The shopping spree that snagged Tagtile and Glancee was just business as usual for Facebook. It buys small companies on a regular basis — almost two dozen over the last two years — to beef up its team of talented engineers, add to the site’s offerings and sharpen competition with rivals.

Because Facebook tends to be tight-lipped about its plans, the company’s string of acquisitions reveals a lot about how Mark Zuckerberg, the chief executive, is charting a course for its future — and potentially sheds some light on what, and who, may be next on the company’s shopping list.

Despite the fast-paced acquisitions, the social networking juggernaut does not generally do a lot of long-term planning for its mergers and acquisitions. “They are a fairly nimble company,” said Paul Buchheit, an entrepreneur who created the first iteration of Gmail for Google and is now a partner at Y Combinator, a popular incubator of tech start-ups in Silicon Valley. “They don’t have a five-year plan for companies they want to buy. When they see a company that makes sense, they focus on getting things done quickly.”

Mr. Buchheit should know. When he sold his start-up, a social network aggregator called FriendFeed, to Facebook in 2009, the deal was completed at a dizzying pace.

“I met with Mark on a Friday afternoon,” he said. “By Sunday night, we’d signed papers and announced the deal on Monday.” It was a similar fast-paced process for Instagram as well.

Mr. Buchheit contrasted Facebook’s agile approach to older technology companies like Microsoft or Research in Motion that scramble to keep up with peers and “miss the boat because they aren’t fast enough to move.”

For example, during the spring of 2010, the Web was ablaze with speculation that Facebook was desperately trying to buy Foursquare, a mobile location-based start-up that was rapidly adding new users and wooing celebrities to its service. But Foursquare’s executives and investors decided it was too soon to sell.

A few short months later, Mr. Zuckerberg and his company quickly swooped in on a fresh target: Hot Potato, another check-in service, moved the company to the Bay Area and assigned its founder, Justin Shaffer, to the job of developing Facebook’s new Places database of restaurants and stores.

Then Facebook lured away an important member of Foursquare, Nathan Folkman, a software engineer, to work on its new Places product.

Facebook declined to comment for this article, citing a need to avoid publicity leading up to the company’s initial public offering expected later this week.

Facebook’s interest in a particular area can hint at a shift in strategy or a new feature of the service. For example, the company’s recent purchase of Tagtile, a customer loyalty service, suggests that the social networking company is gearing up for a move into e-commerce and coupon deals, an area that Google, Amazon, eBay and Foursquare have begun to dabble in.

The theory has proved correct in the past. For example, in early 2011, Facebook went on a design binge, collecting Snaptu, Sofa, Push Pop Press and Strobe, all companies that produce information graphics and layouts.

As it did with Places, it also cherry-picked talent. Lane Becker, who helped start Adaptive Path, a user-experience consulting firm, said that he was impressed by how efficiently Facebook was able to reel in so many prominent designers, including Mike Matas, who worked on much of the software for the original iPhone and iPad, and Rasmus Andersson, who led design at Spotify, the streaming-music service.

“It was an amazing approach to draw the best people in,” he said. “Designers want to work with other designers.”

The Web buzzed in April last year when Facebook picked up DayTum, the start-up of Nicholas Felton, a designer known for his meticulously and beautiful annual reports that chronicle the ins-and-outs of his life.

Then, in September, the company introduced its sweeping site redesign called Timeline.

Most recently, the company brought on Wilson Miner, the lead designer at Rdio, a streaming-music service, as well as Elizabeth Windram, a former user-experience designer at Yelp, YouTube and Google Maps — a move that, according to Mr. Becker, seems to indicate the company is about to beautify its mobile applications, which many have called unattractive and difficult to use.

“In the mobile space, design is everything,” he said.