In one of the attacks a 14-year-old victim was stabbed in the chest and leg and kicked in the head.
Bryan Kiggwe, 18, was part of a gang which carried out the series of robberies over a month long period.
Kiggwe, of Harehills Avenue, Harehills, was sentenced to six years and three months in custody at Leeds Crown Court after he pleaded guilty to 14 offences committed in January and February this year.
In one of the offences a 14-year-old boy was stabbed twice.
The victim had been approached by Kiggwe and an accomplice in Old Lane, Beeston, at 6.40pm on January 16.
He was threatened with a knife and demands were made for his valuables.
The victim tried to escape but was pushed to the ground and kicked in the head before further demands were made.
As he continued to resist, he was stabbed in the chest and leg, fortunately causing only minor injuries.
The knife was then held to his throat and he was forced to hand over this phone and give his passwords.
On January 28 Kiggwe was among a group of five suspects who targeted four victims, aged 14 to 20, in Assembly Street in Leeds city centre.
They surrounded the victims, threatened to stab them and produced a knife.
One victim was dragged to the floor where his head was stamped on and kicked.
A 21-year-old man was targeted by Kiggwe and an accomplice in Beeston as he walked home from work on January 8.
They dragged him into Cross Flatts Park and produced knives before kicking and punching the victim while making demands.
He was forced to hand over his valuables, including his phone and wallet.
The victim had to attend hospital for blurred vision as a result of the attack.
On January 9, Kiggwe and another male approached a 25-year-old man in Dewsbury Road, Beeston, and told him they had a knife and wanted money.
He handed over his phone and valuables and was pushed to the ground before they ran off.
Kiggwe pleaded guilty to eight counts of robbery, two counts of possession of a bladed article, three counts of fraud and one of possession of cannabis.
Kiggwe’s barrister, Robin Freize, told the the court the defendant was aged 17 at the time of the offences and pleaded guilty at an early stage
Mr Freize said Kiggwe came from a supportive family and was now trying to further his education while in custody.
Detective Inspector Andy Norgate, of Leeds District Crime Team, said: “The offences that Kiggwe has been convicted of include incidents where significant violence was used and victims were put in genuine fear.
“They were punched and kicked and threatened with knives, and, on one occasion, a 14-year-old boy was stabbed.
“These were terrifying incidents for the victims and we hope they will be able to take some comfort from knowing that he has been caught and given a lengthy period of imprisonment.
“He has shown absolutely no remorse for his actions and only admitted his involvement when faced with the weight of evidence that was painstakingly gathered by the investigating officers.
“We are still progressing active lines of enquiry in relation to the other suspects involved in these offences.
“Crimes of this nature, particularly where knives have been used, cause understandable concern in the community and we want to reassure people that we will always treat them seriously and investigate them fully to ensure those responsible are brought to justice.
“We hope the significant sentence that Kiggwe has received will send a very clear message to others who think they can commit offences like this without having to face the consequences.”