RNA - The march, dubbed the "White Allies Only" rally by its organizers, took place Thursday evening from a downtown plaza to Busch Stadium.
The crowd stood outside the stadium chanting for several tense minutes while about 100 officers stood inside a metal barrier, some in riot gear.
A judge acquitted former officer Jason Stockley on September 15 in the 2011 shooting death of Anthony Lamar Smith. Stockley, 36, killed 24-year-old Smith after a police chase.
Protest organizer Cori Bush said the point of Thursday's rally was to emphasize that it isn't just African-Americans upset by police violence against blacks.
"I think it's great for people to know there are white people that believe black lives matter and aren't afraid to show it, that want to tear down systemic racism," Bush said.
Jennifer Sherer, a demonstrator from St. Louis, said the city remains badly segregated. "When you look at the history of St. Louis, the racial divide is very intentional," she said while holding a "Black Lives Matter" sign.
In a separate protest, a couple hundred demonstrators blocked traffic for about 30 minutes Thursday afternoon near Forest Park.
Thousands of protesters marched in St. Louis for several nights last weekend. More than 160 people were arrested in those demonstrations after they turned violent.
The protests have evoked memories of the riots following the 2014 shooting of an African-American teenager by a white officer in nearby Ferguson, Missouri.
The St. Louis Post-Dispatch reported that there have been more fatal police shootings in St. Louis so far in 2017 than in any year for a decade, even with three months remaining until year's end.
US police departments have been under heightened scrutiny in recent years for the disproportionate number of police killings of African Americans.