Sam Clafin spoke about Catching Fire and playing Finnick on Future Radio which released a transcript. Apparently he had never even heard of Finnick before auditioning for the role?
Beth: He was one of my favourite characters and he has one of the biggest arcs. Was he one of yours? Did he stand out while you were reading, like you struck gold that you got the good part?
Sam Claflin: I mean for me, I was already kinda cast! He definitely stuck out somewhat but for all the wrong reasons. Very selfishly, that was the only character I really cared about [laughs]. But the great thing about the books is that Suzanne Collins created these great arcs for each and every character, no matter, I mean from Katniss all the way down to her sister, to her mother. You know, each character goes on a journey. And I think that’s what’s so riveting about the books themselves.
Source: The Hob