The usual response from a "THANK YOU" would be:
"You are welcome."
But it also varies to the person you are talking to.
If for a FRIEND (a buddy) you may say: "That's nothing dude."
If for a younger BROTHER, you may say: "I deserve a pay back, bro"
If for your GIRL FRIEND, you may say: "Sssssh Don't say thank you, say I love you."
If for a CUSTOMER, you may say: "Come back next time!"
If for an ENEMY, you may say: "Watch your back, I'll kill you next time."
If for a RELATIVES, you may say: "It's a responsibility."
But for real friends they don't usually use "thank you" and need not to say a welcome back, they just help without a return.