(Adds comment from county prosecutor)
By Nick Carey
FERGUSON, Mo., Aug 15 (Reuters) - Protests over the shooting of an unarmed black teen in Missouri were boisterous but peaceable on Thursday night as a small number of state police, led by a newly appointed black captain, replaced riot gear-clad local forces and mingled with the crowd.
Hours earlier, Missouri's governor Jay Nixon put Highway Patrol Captain Ron Johnson in charge of security in the town of Ferguson after almost a week of clashes between protesters and police firing tear gas and stun grenades. Dozens of people have been arrested amid looting, shooting and vandalism.
In a tactical U-turn, Johnson, and a handful of black officers without body armor walked among thousands of protesters filling the streets of the mostly black St. Louis suburb, demanding justice for the killing of 18-year-old Michael Brown.
"We just want to be able to come and demonstrate together without the fear of being shot. It's that simple," said 53-year-old protester Cat Daniels, an Iraq veteran. "What you see tonight is people coming together. When that kid was killed the hurt and the pain was real."
Mark Hall, a 21-year-old student, said: "I'm so happy they left us alone so we could prove that all we wanted was the opportunity to exercise our rights peacefully ... a chance to be heard."
In the forecourt of a gas station burned out during this week's rioting, a cowboy rode a horse and a group of children danced on pavement covered in chalk drawings with the words: "Now the world knows your name, RIP Mike."
Elsewhere drivers honked horns and waved signs in solidarity and one group of demonstrators even took to the streets on a car-sized replica of fictional steam train Thomas The Tank Engine.
"It's because of this young man right here," Johnson, who grew up in the Ferguson area, told a CNN reporter, as the captain held up a picture of Brown to shouts of approval from protesters around him. "It's about the justice for everyone."
The protests have cast a spotlight on racial tensions in greater St. Louis, where civil rights groups have complained in the past that police racially profiled blacks, arrested a disproportionate number of them and had racist hiring practices.
Two thirds of the town's population of 21,000 are black while 50 of its 53-strong police force are white.
Brown's shooting galvanized a national moment of silence and rallies in other U.S. cities.
In New York, a large crowd briefly overwhelmed a small police presence in Union Square park, forcing officers to scramble to close one of Manhattan's major thoroughfares. Local media showed a handful of protesters being arrested.
In St. Louis, CNN footage showed hundreds of people peacefully assembled in the shadow of the renowned Gateway Arch, Brown's mother and other family members among them.
Seeking to defuse the situation, U.S. President Barack Obama had called on police to respect peaceful demonstrations.
Nixon said Ferguson lately "has looked a little bit more like a war zone, and that is unacceptable".
Police have pledged to do better but have also justified the tough tactics, saying they have responded to the threat of violence during protests.
"WHAT'S HIS NAME?"
Protesters have decried what they say is a lack of transparency from police investigating Saturday's shooting, including the refusal to name of the officer responsible.
On Thursday night in Ferguson, about 200 demonstrators chanted, "What's his name? What's his name?'" at Johnson and the St. Louis County police chief, Jon Belmar.
Police said they plan to release the officer's name on Friday, according to CNN and Los Angeles Times reports.
Some critics have also called for St. Louis County Prosecuting Attorney Bob McCullough, who was critical of Nixon's move, to be taken off the case.
"He had no legal authority to do that," McCullough was quoted as saying by the St. Louis Post-Dispatch newspaper. "For Nixon to never talk to the commanders in the field and come in here and take this action is disgraceful."
U.S. Attorney General Eric Holder said in a statement that police had accepted an offer of technical assistance from the Justice Department on crowd control and public safety "without relying on unnecessarily extreme displays of force".
A law enforcement official told Reuters that Holder expressed his personal condolences for their son's death in a phone call with Brown's parents and promised the department would conduct a full, independent civil rights investigation.
Early on Thursday, a member of the Anonymous hacker activist collective tweeted the name of a person alleged to be the police officer who shot Brown. But police and other Anonymous tweeters said the activist had named the wrong person.
There is little clarity on what occurred during Saturday's incident. Police have said that Brown struggled with the officer who shot and killed him. The officer involved in the shooting was injured during the incident and was treated in a hospital for swelling on the side of his face, they said.
But some witnesses have said that Brown held up his hands and was surrendering when he was shot several times in the head and chest. (Additional reporting by Brendan O'Brien in Milwaukee, David Bailey in Minneapolis, Carey Gillam in Kansas City, Jeff Mason in Edgartown, Mass., Curtis Skinner and Brendan McDermid in New York; Writing by Eric M. Johnson; Editing by Louise Ireland)