Sonia Carter, head of social and digital media for Mondelez Europe, rifles through her bag in search of a French Carambar. She wants to share her favorite Mondelez product, but it's not there -- she appears to have eaten it. "You never, ever grow out of the magic of sweets and chocolate," she laughs apologetically.

Ms. Carter works across Kraft-owned Mondelez International's biggest territory, Europe, which covers 33 markets. Last year the U.K. success of her Cadbury Creme Egg digital campaign, made up of a series of one-off posts that created a narrative thread, brought about a shift in the confectionery giant's social media strategy.

The Creme Egg results showed that a combination of paid and viral content on Facebook drove the same purchase consideration -- 20% uplift -- as TV, but with a third of the investment. As a result, the new "storytelling at scale" strategy was born.

"I've always been very pragmatic, so the reason I'm excited about storytelling at scale is because it's about results," Ms. Carter said. "It's not about doing digital for the sake of digital -- it's about really, really affecting business change by talking to millions of people."

Ms. Carter knows that her brands are competing with a sister's party or a friend's new baby when trying to get people engaged with their content. "We're always looking at bigger, better and more creative ways to have the most impact. It's imagining that every single one of your posts is as important as a slot in 'X Factor'," she said.

Social has become even more important to Mondelez since the Facebook deal, which is a big focus for Ms. Carter. She said, "Facebook is the largest social network by far for Europe. So in formalizing our partnership we get media value, creative support, and innovation opportunities."

Originally Ms. Carter wanted to make music videos, but realized she was about 20 years too late to be a pioneer in the field. She chose instead to be an internet pioneer, and became a self-taught web designer for many years before moving to an agency in Sydney, Australia (now part of Y&R) and earning a masters in internet communication.

Ms. Carter joined Mondelez in January 2011 as head of digital and new media at Cadbury U.K., working on the London Olympic sponsorship. It was soon after Twitter and Facebook opened up to paid tweets and posts, and Ms Carter's team created an inflatable Cadbury House in London's Hyde Park. Around 50,000 people visited the house, but more than three million were able to experience it via social media, thanks to check-in stations on site.

For pan-European campaigns, Mondelez develops content centrally -- Milka's "Dare to be Tender" campaign, for example, ran "101 Tender Dares" across 25 markets on Facebook -- but local markets are allowed to adapt executions. "It's not dictatorial -- you need flexibility to react to cultural events or local interests," Ms Carter said.

After Oreo's famous Super Bowl moment, Mondelez and Kraft marketers have a lot to live up to in real time marketing, but Ms. Carter is not looking for chances to replicate its success. She said, "Every brand is trying to do an Oreo, but for me, real time marketing is not necessarily about responding to the big moments, because the likelihood of success is very small. It's much more local, more authentic, much more responding to something in the moment that makes sense for your brand or for your community. It's not necessarily about setting up war rooms."

During the Brit Awards (the U.K.'s equivalent of the Grammys) in February, Cadbury prepped posts in advance. The brand was connected to the Brits by the presenter, James Corden, who was also the star of Cadbury's ad campaign. Tweets included a Pharrell Williams hat made out of chocolate chunks, and, when Bruno Mars won an award, a post saying, "This is the only time you'll see Cadbury's congratulating Mars. Well done Bruno."

Digital marketing for Ms. Carter doesn't mean following consumers around and bombarding them with messages. Instead she wants to make sure that her brands fit in to existing consumer behavior. "Digital is 24/7 and if people wake up in the middle of the night, the first thing they do is grab their mobile phone and look at Instagram or YouTube, so they're choosing when they want to engage with us," she said. "We just need to make sure that we are there and fitting in with what they're doing."