I've seen someone respond with "They're welcome" to "X says thanks" where X is another person and/or group of persons. The reply seemed okay to me, but its correctness has been immediately contested by a few others.
The fact that I cannot find instances of it being used anywhere on the web got me to doubt my initial belief, and now I'm starting to think it's some sort of rookie mistake that nobody (else) does.
There are no real arguments given by the people contesting its correctness, but I don't have any to support its correctness either. My guess is the confusion started because "You're welcome" is always translated as "Cu placere" in Romanian, which literally means "With pleasure" rather than "You're welcome (to...)". Even so, the expression still seems appropriate.