I remember visiting this website once...
It was called Haikyu!! Popularity 民意调查 - Haikyuu!! Wiki - Wikia
Here's some stuff I remembered seeing:
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There have been three official character polls: two conducted by
The first popularity poll was released in Chapter 57 with a total of 26,370 votes.
Kiyoko Honda (the fake Kiyoko) (128 votes)
The second popularity poll was released in Chapter 123 with a total of 53717 votes.
Takara Tomy, a famous Japanese manufacturer of anime merchandise, conducted an official popularity poll on its website. The voting took place from May 12-May 31, 2014, with 560,584 votes cast.