Among the speakers were Warmbier's brother, Austin, his sister, Greta, and a few of his friends.
"This college kid never should have been detained in the first place", said Portman, who previously revealed that he met secretly with North Korean officials in NY last December to press for Warmbier's release.
Doctors in the US said Warmbier had severe brain damage and was in a state of "unresponsive wakefulness".
Warmbier. 22. was sentenced to 15 years hard labor in North Korea for allegedly stealing a propaganda poster from his hotel in early 2016.
Kenneth Bae, an American who was jailed for almost two years in North Korea, told CNN he believed Warmbier could have been tortured, and cautioned other Americans against going to North Korea.
A spokesperson for the Department of State said last week that Rodman's visit to North Korea had nothing to do with Warmbier's release.
"Although we had no reason at all to show mercy to such a criminal of the enemy state, we provided him with medical treatments and care with all sincerity on humanitarian basis until his return to the USA considering that his health got worse", the agency quoted an unnamed spokesman of Pyongyang's Foreign Ministry as saying.
"The fact that Warmbier died suddenly in less than a week just after his return to the USA in his normal state of health indicators is a mystery to us as well", the agency reported. He was in a coma and died Monday.
"He had a deep desire to know God in a personal way", Mr Thomas said.
"The smear campaign against (North Korea) staged in the USA compels us to make firm determination that humanitarianism and benevolence for the enemy are a taboo and we should further sharpen the blade of law", the spokesman added.
The North had earlier Friday denied torturing or mistreating Warmbier, in the first official reaction to his death. They have blamed his death on the "awful, torturous mistreatment" he received in North Korea.
It demanded that South Korea return 12 restaurant workers who defected to the South past year.
On June 15, during his congratulatory remarks in a local ceremony that marked the 17th anniversary of the June 15th North-South Joint Declaration of peace and prosperity, Moon said he was willing to "sit knee-to-knee, head-on-head" with North Korea to discuss ways to implement the past joint inter-Korean declarations if Pyongyang refrained from conducting any additional missile or nuclear tests.
Journalist Isaac Stone Fish uses the incident to describe the world of Western tourism in North Korea, in which carefree college students sometimes find themselves clashing with a closed and repressive state.
Chris Volo, Rodman's agent who accompanied the athlete on his trip to North Korea, told ABC News that before they went, "I asked on behalf of Dennis for his release three times".