The sister agencies are to work on integrated global campaigns across traditional and digital PR, they said in a statement.
This will include identifying influencers across different markets for the Sanpellegrino portfolio, which includes water brands S.Pellegrino and Acqua Panna, along with Sanpellegrino Sparkling Fruit Beverages.
The account was previously held by Ketchum. We Are Social and Citizen were appointed following a competitive pitch.
The statement added: "Sanpellegrino has made the appointments in recognition of the integration between traditional and digital PR and the high level of strategy and creativity required across these ever more connected disciplines. We Are Social will work on this project together with sister agency Citizen Relations during an exciting period marked by strong innovation within the Sanpellegrino brand portfolio."
The joint win follows changes last year that saw We Are Social and Citizen Relations join a new marketing services group following an agreement between BlueFocus and US data analytics firm Fluent Inc (until April known as Cogint).