Many times when an artist goes viral, they are unable to follow up with another hit. Or if it is a hit, it is nowhere near the level of impact as its predecessor.
Here are a few times where artists were able to keep the momentum up
Apink: No No No-Mr. Chu
EXID: Up&Down-Ah Yeah
Twice: Cheer Up-TT
Hwasa was probably the only artist here to have an even bigger viral hit the second time around. Also Twice depending on who you talk to.
Any others you can think of?