It was held Sunday night outside Red Eye Gallery, where he worked.
"Julian was a community leader. You don't see this type of turnout with just anybody," Kevin Barnett said. "He was really rooting for this community, and we just lost another great person."
Investigators say Issac disappeared last Tuesday in southeast Houston after taking an Uber to visit his girlfriend.
ORIGINAL STORY: Houston tattoo artist missing after taking Uber to see girlfriend a few days ago, brother says
During a search by Texas Equusearch Saturday, a body was found.
The medical examiner has not confirmed that it's Issac, but detectives tell ABC13 they are pretty certain it's him based on clothing he was wearing when he was last seen.
Around 1 p.m. on Saturday, a neighbor called police to report a strong odor in the 11700 block of Teaneck Drive, around the same area crews were searching for Issac.
The neighbor told authorities that they originally thought the smell was from a dead animal, but later told police they saw a person's body.
Officials with Houston Homicide Division and Missing Persons Division were called to the scene where they confirmed finding the body.
Det. Kyle Heaverlo said a kidnapping was reported in that same neighborhood this past Tuesday.
Heaverlo said officers found several items belonging to the person who was reportedly kidnapped in that area.
READ MORE: Body found less than 2 miles away from search for missing Houston tattoo artist
After three days of search efforts for the missing person, Heaverlo said he and other officials determined that the person was indeed missing. However, evidence and surveillance video suggested he was not taken against his will or "forcefully removed."
On Saturday, Texas EquuSearch joined the effort to find Issac who was last seen on June 15.
He took an Uber to visit his girlfriend in the Sagemont area around I-45 S and the Beltway, said his brother, William. He was last spotted in the 11700 block of Teaneck Drive.
Texas EquuSearch volunteers fanned out in the area of Teaneck after staging at Burnett Elementary School. Searchers on foot and on ATVs were part of the initiative.
Before he disappeared, Issac reportedly called his mother and William saying that he was being chased and that he was going to get killed.
Police told family members that a neighbor's surveillance video shows Issac's hat and phone in a yard, his brother said.