Thirteen Madness fans had their mobile phones stolen in the crowd at Sunday’s gig at the County Ground in Northampton.
Northamptonshire Police said some fans also had their cash and wallets stolen at the concert, which was attended by about 12,000 people.
Madness fan Leanne Francis, of St James, contacted the Chron about the incidents, and said she believed the thefts were the work of an organised gang.
She said: “The gig turned into a complete nightmare.
“It’s such a shame as Madness were brilliant, but from halfway through the concert the atmosphere was ruined for a lot of people just because of a few idiots.”
A police spokesman said: “We have had 13 reports of mobile phones being stolen from people’s pockets at the Madness concert. Some people also had cash and wallets stolen from their pockets as well.
“No arrests have been made and we would of course appeal for anyone with any information to contact us on 101.”