That is not enough context. e.g. "You've found them!" could be an exclamation made by a 3rd party in seeing the person returning with their lost siblings. "You'd found them" could be narrative related by the character to the reader. We need the paragraph or surrounding sentences where you want to use this.
– SamApr 16 '15 at 14:41
1
"You've found them" is correct. "You'd found them" is correct. "You'll find them" is correct. "You'll have been finding them" is correct. This is like asking if it should be "you found him" or "I saw her". Both are correct. They just mean entirely different things.
– RegDwigнtApr 16 '15 at 14:43