Police said three teenagers were walking on Logan Road near the intersection of Bardsley Avenue in Greenslopes on Tuesday night when they were approached by two men who demanded their belongings.

Brisbane Times understands the teenagers had attended their formal and had been at an after-formal party before they were confronted by the men.

One of the teenagers ran but the remaining pair were attacked.

One was stabbed twice in the back and the other was struck several times with a handgun.

The men stole a wallet, smartphone and a bag and then left on foot. Police believe the men might have entered a dark-coloured vehicle nearby.

The injured teenagers flagged down a passing police car just after midnight.

It was understood at least one of the boys suffered an internal blood clot following the blow to the head.

They were taken to the Princess Alexandra Hospital.

The men were described as African in appearance, aged in their early 20s and wearing black, baggy clothing with baseball caps and hoods covering the caps.

Police said one of the men was about 190cm tall and the other had short, braided hair.

Detective Senior Sergeant Warren Gibbs said the teenager who received stab wounds from a 27-centimetre-long kitchen knife remained in hospital in a stable condition to be monitored but did not need surgery.

He said police were urging anyone who may have seen a dark blue Honda sedan at the time of the incident to come forward.

"Shortly after (the incident), police who were in the area at the time observed a dark blue-coloured Honda Sedan and it was leaving from Logan Road, Greenslopes at speed," he said.

"...We know that car was seen leaving at speed and when attempted to be evaded by police, they evaded police."

Detective Senior Sergeant Gibbs said the teenagers were lucky the officers were there at the time to help.

"It was fortunate that police were there at the time and they actually flagged down the police officers, who the ones that saw the vehicle leave at speed," he said.

Detective Senior Sergeant Gibbs said the attack was opportunistic and caught the teenagers "by surprise".

"(The teenagers) didn't instigate anything," he said.

"They were simply walking one particular location to another to have a good time in the evening and they were approached by these two males and assaulted and had their property stolen."

Detective Senior Sergeant Gibbs said the incident was a shock to the teenagers.

"Everyone, whether it be young boys or not, has got the right to walk around in the streets and feel like they can be safe and clearly not be attacked and have their property stolen," he said.

"It was no doubt a shock for them and they are certainly reeling from that experience and we as a police are very keen to investigate it and try to identify who the attackers were."

Detective Senior Sergeant Gibbs said it was very concerning a hand gun, described as similar to the kind police had, was in the wrong hands.

"We certainly don't want people who are capable of stabbing someone to have this in their possession," he said.

Detective Senior Sergeant Gibbs said it was unclear the exact words that were said during the attack but there was a demand for property.