Question: Pentatonix, the five-member American a cappella group lost their vocalist Avi Kaplan in 2017 at the same time as their tribute to which group received over 250 million views?
Sentence (from "Avi Kaplan"): Avriel Benjamin "Avi" Kaplan is an American singer and songwriter, most well known as a past member of the a cappella group Pentatonix.
Relevant evidence: Yes