"We have so far arrested the promoter of that New Year concert. We are also actively searching for other organizers and promoters," police spokesman Fred Enanga said.
Authorities say the party-goers were killed at Freedom City mall in Kampala as revelers thronged a single exit to watch a midnight fireworks show.
Four other exits had been ordered shut by the promoters and investigators were looking at whether "negligence" was to blame for the loss of life.
"The revellers had one point of entry and exit. Therefore several victims were trapped and trampled upon through the narrow passage which became a bottleneck for many, mostly juveniles."
Most of the victims were aged between 10 and 20, police said.
The promoter is well known in Kampala for staging major festivals.
In 2009, one person died and three were injured in a stampede at Kampala's Kansanga amusement park.