Roaec was the son of Carc, and as such "a descendant of those [ravens] that had remained on the hill even after Smaug had driven out their old allies, the Dwarves".

Roaec does not explicitly appear. However, just prior to the final confrontation with the Elven Army assembled before the gates, a raven is seen flying away from the gate of Erebor, then just before Dáin's Army of Dwarves arrives, the raven is seen flying back to Thorin at the gate. This visually implies that Thorin sent a message with this raven, though it is not explained in dialogue, and the raven itself does not talk.
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FROM 216.240.30.*