A Muslim student group organized a vigil to pray and have a moment of silence for Mueller, hoping she is still alive.
One man who was there said he knows Kayla personally and says she was always someone who wanted to make a difference by helping others.
A group gathered Monday night at the Hayden Library Lawn on the Arizona State University main campus. They held a candlelight vigil showing their support for 26-year-old Kayla Mueller and prayed for her return.
Mueller, who is from Prescott, was taken hostage by ISIS in August 2013.
Among those at the vigil was a man who says he went to high school and college with Mueller.
"I hope she's still alive. I know that their still hope that we're clinging onto, all of us, that she is not dead," said Timothy Scipio.
The vigil was organized by Seema Kassab, the President of the ASU Muslim Liberty Project. She's hoping to spread the word that ISIS and other Muslim radicals are not representative of her religion.
"I am so thankful for the work that Kayla did, it hits home so much because she's helping the suffering Syrians, my family is there so the work she is doing worked to help our cause," said Seema Kassab.
Others at the vigil who are not Muslim and did not know Kayla showed her family and the world that Kayla's work will not be forgotten.
"Being out here supports them, that matters a lot, especially the whole country. That's why I decided to show support," said Liam O'Neal.
Timothy says even in high school Kayla was someone he knew would try to help anyone who was suffering.
"She was very... she was very always happy to lend a hand, help out anyone, whoever that might be," said Sapio.
The candlelight vigil also remembered and honored the other victims killed by ISIS including the Jordanian pilot who was burned alive last week. In response, Jordan has launched more than 50 airstrikes against ISIS targets.