The website staged a pitch for PR support without informing four-year incumbent Beatwax Communications.
The agency was only alerted to the firm's decision to review the account after the pitch process was complete.
BMA Communications won a four-way pitch this week to handle national consumer campaigns for the company on a project basis.
But fees on the account have been cut substantially after a decision to take much of PR in-house. "There was a disagreement over fee structure which brought to head the change of agency," said Beatwax head of PR Paul Johnson. "It's not because we've got a sour relationship with them."
BMA will focus on raising the profile of the firm's spin-off sites, Genes Reunited and Friends Reunited Dating, as well as devising campaigns for the main site.
Friends Reunited has amassed 11m members through word-of-mouth and media coverage, based around co-founders Steve and Julie Pankhurst and stories of reunions.
Friends Reunited head of PR Carolynne Bull-Edwards said: "Following the global expansion of our brand, we have brought most of our PR in-house, where it is more cost-efficient and we can grow our own expertise."
Bull-Edwards, who joined two months ago, hired Elizabeth Sheahan as its first press officer this month.
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