The victims were offered deals to trade mobile phones but had their cars stolen at knifepoint, once arriving at the meeting points in Wolverhampton.
They were confronted by two offenders who ambushed them and took the vehicles during the robberies which happened earlier this week.
The first offence saw a 31-year-old threatened with a knife before his Toyota Aygo stolen in Lawrence Avenue, Heath Town, at around 6.20pm on Monday.
The following day, which was yesterday, a 20-year-old man was assaulted at knifepoint in the same street at 2pm before his Fiesta was taken, which was later recovered.
Following enquiries, the 17-year-old was arrested on suspicion of robbery offences and was in custody for questioning on Wednesday night.
He was also being quizzed about an attempted robbery involving a similar tactic in Park Village in December.
Chief Inspector Hasson Shigdar, from Wolverhampton Police, said: "We know this is a time of hardship, with people at even greater risk of being exploited and lured into vulnerable situations.
"But it’s now important to stay clear of such situations for two very important reasons.
"You could be putting yourself in danger of harm, but also breaking the lockdown rules which are there to stop the spread of a deadly virus.
"These robberies were deplorable crimes where the targets have faced the fear of being badly injured.
"We will be supporting them through their traumatic ordeals, and reminding them of the need to follow restriction rules."
The investigations are ongoing.
Anyone with information is asked to contact police, quoting crime reference number 20WV/17406A/21.