Aisha (may Allah be pleased with her)when she was told that her neighbours said: Barak Allah feekum (may Allah bless you) she told her maid to reply to them by saying:

May Allah bless you too

Note:
*Bellow are the three forms (you sing., you plur. present sense and you plur. absent sense)

[For a male]
wa feeka baarak-allaahu

[For a female]
wa feeki baarak-allaahu

[For a group of men]
wa feekum baarak-allaahu