Daequan George is described as black, 4ft 8ins tall, of medium build with short black hair. He was last seen in Tottenham.
19 year-old Abdul Al-Faisal was arrested after trying to get into his school to retrieve his favourite hat.
The police watchdog says it is trying to contact key witnesses to the shooting of Mark Duggan, who have so far refused to be interviewed
In a statement, The Met Police said: "There was a licensed community event in Marksfield Park, Tottenham. Unknown to the locals, police, a small, extreme nationalist Polish group, Zjednoczeni Emigranci had also planned an event nearby.
"Taking the peaceful community event by surprise, Z.E. launched an unprovoked attack, hurling verbal abuse at locals, intimidating the children and families that were present, before turning to physical violence."
About 150 of us were having a party in Markfield Park in Tottenham, Neo-nazi polish fascists turn up, full scale riot operation
After a neo-nazi attack in Markfield Park, Tottenham, yesterday during a music event, join our UAF rally today 6PM @ Tottenham Town Hall
A man was stabbed in a suspected 'neo-Nazi' attack when Polish extremists stormed a public party in a park packed with families. Violence broke out at a community event when thugs - thought to be members of a nationalist group - began hurling rocks, flares and glass.
Around 150 are thought to have been at the music festival in Markfield Park in Tottenham. A 24-year-old man was taken to hospital after being stabbed, and was later released.
A nine-year-old boy who went missing from a playground has been found. Daequan George was found safe and well by officers of the Metropolitan Police in north London at around 11.30 today.
He had not been seen since 8pm last night after visiting a playground in Stamford Close in Tottenham.
– Det Supt Stephen Clayman, Met Police
The playground is very close to his home address. He plays out but has never gone missing before overnight - but has gone missing previously.
When we've spoken to people nearby they didn't know his name but when we showed a photo they knew who he was as a local boy.
Last night, a lot of searching went on with the helicopter and street searches. But we're now retracing our steps and carrying out new searches.
Police are searching for a nine-year-old boy who has gone missing from Tottenham.
Given his age, officers say they're growing increasingly concerned for his wellbeing.
Daequan George is described as black, 4ft 8ins tall, of medium build with short black hair. He was wearing yellow or rust-coloured jeans, a black zip-up hooded top with leather patches, a purple and yellow hat and black Nike trainers which have a green 'Nike tick' on the tongue.
Anyone with information is asked to call police on 101.
A mother who died after being stabbed in the neck in broad daylight has been named as Naudel Turner. The 42-year-old was attacked near a GP surgery in Tottenham where she worked as a nurse. She travelled to work in north London from her home in Fulham.
– Metropolitan Police
Ms Turner was a hard-working mother of two boys. We now believe she knew her attacker. I need to hear from anyone who was in the Bruce Grove area shortly before one o'clock on Wednesday, 19 March and who may have witnessed the incident.I would like to directly appeal to anyone who may have captured images or footage before and after the incident to contact us immediately.In particular we would like to speak to a black male who was wearing a white tracksuit top who witnesses saw taking images at the scene.
Police in Tottenham are appealing for witnesses to the murder of a woman stabbed to death in broad daylight yesterday.
The 42-year-old victim was knifed in the neck near Radley Road just after 1pm. Detectives are asking anyone who might have caught the attack on their phone to come forward.
– DCI Noel McHugh
"I need to hear from anyone who was in the Bruce Grove area shortly before one o'clock and who may have witnessed the incident.I would like to directly appeal to anyone who may have captured images or footage before and after the incident to contact us immediately."
The 42-year-old victim was taken by ambulance to a central London hospital where she was pronounced dead. Officers believe they know the identity of the deceased, but await formal identification.
Next of kin have been informed.