This is a pretty common expression in Korean although I only get to know what it means a little late while I was talking to a Korean friend. I was so upset then and he said to me this phrase — 힘내요 (himnaeyo).
It means cheer up! It also means the same as the cliche ‘break a leg’ in English. When you want to uplift someone’s spirit or give encouragement, this is a good expression to say. To someone esteemed, one can say the more polite way 힘내세요 (himnaeseyo). This is in addition to common expression like 화이팅 (fighting) or 아자 (aja).
*image was taken from firemasterxd.devianart
It Started with Hangul 
Janey, it’s 3:30 AM And I’m sitting here listening to TVXQ and feeling pretty depressed, and you show up in my email, telling me to 힘내세요 ! And you know what? It worked! Thanks! I feel a lot better. 😉
good to hear that =) you do love TVXQ