Originally, Ye Feng intended to have a heart-to-heart talk with Voldemort. To his great disappointment, however, Voldemort still hadn't come to visit by this point in the semester, which left Ye Feng with no choice but to pass the "opportunity" meant for him on to someone else.
On the very night he finished refining the healing pills, Ye Feng quietly slipped over to Lupin's dormitory. The reason he hadn't gone straight to Sirius Black was simple: he didn't know the man, nor did he know where Sirius was currently hiding.
He didn't have the Marauder's Map like the twins did, so trying to find someone was a bit difficult.
Chapter 177