Keon was attacked in Linwood Road, in the Handsworth area, on the afternoon of Thursday, January 12, by a group of youths.
West Midlands Police officers have already arrested five boys in connection with the killing. Three boys, all aged 14 years old, have now been released under investigation.
On Wednesday morning, police confirmed that two boys, aged 15 and 16 years old, remain in custody and detectives had been granted extra time to question them.
Detective Chief Inspector Alastair Orencas, from the force's homicide team, said: “This is a complex investigation which continues at pace, we are determined to find out exactly what happened to Keon and who was responsible.
WATCH: Family of murdered Keon Lincoln issue appeal to help catch his killers
“I know there are many concerns and worries within our communities, but please be assured we are doing all we can and will not give up in our pursuit to get justice for Keon and his family. We have a dedicated team working on this 24/7.
“However, I still need your help - the community will be vital in helping us – I need anyone who’s not yet spoken to us, to do so, as soon as they can.
“This week, we heard just how devastated Keon’s mother, sister and their wider family are in their moving and brave appeal. Imagine if that was your relative? So, if you know something, please do the right thing and tell us."
Anyone with information is urged to call West Midlands Police on 101, or Crimestoppers anonymously on 0800 555111.