The partnership will see characters in using Sure Girl, which Unilever recently launched as an antiperspirant deodorant for the teenage market.
Bebo users will be encouraged to send in articles in the theme of "What makes you sweat?" with the chance of winning a cameo role in the drama.
Users will also be able to become friends with the brand through a dedicated profile page.
The deal was brokered by Mindshare Performance and digital division Mindshare Interactive and marks Unilever's first move into brand integration with a social network.
'Sofia's Diary' launched exclusively on Bebo earlier this month and follows the life of 17-year-old Sofia Taylor, played by 'The Bill' actress Rachel Hyde-Harvey, as she moves to London to live with her father and his new family.
Each weekday Sofia and her friends update their video diaries with two to three minute instalments, as well as their own Bebo profiles, so that the audience can follow the story and engage directly with each character.
Claire Gomm, senior brand manager at Unilever, said: "The partnership with Sofia's Diary is ideal for Sure Girl as it allows us to engage in a dialogue with the brand's core teen audience and make an emotional connection with them that can be far deeper and more resonant than via traditional media spend."
Ziv Navoth, Bebo's vice president of marketing and business development, said: "The growing success of Bebo's entertainment properties demonstrates the potential for brand owners such as Unilever to engage with and develop long-term relationships with consumers in the social media environment."
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