Pearls, gold chains, and other items worth nearly Â£4,000 were stolen when a group of two men and three women distracted staff at Crown Jewellers.
The burglary happened on September 6 at around 1.20pm, and cash was also taken.
Sue Kramer, who has owned the shop on Commercial Street for 18 years with her husband Stephen, said: "For a lot of businesses on the high street, times are tough, so it's very sad when people think it's acceptable to go and target businesses.
"People have to work jolly hard to make their money nowadays. And it's not just the fact that it's happened - it can make you nervous afterwards, when people come into the shop."
Police are appealing for information about the incident, and Sue and Stephen said the response and support from their customers has already been overwhelming.
Sue said: "Sometimes it's only when something like this happens, that you realise how much people think of you, and we can take heart from that. The response from our customers and friends has been amazing, they've been so kind and concerned.
"We were in complete and utter shock when it happened, we were absolutely devastated - nobody wants to go through something like that. But it could have been a lot worse. It was the audacity of them, they were as bold as brass."
A North Yorkshire Police spokesperson said: "It was a burglary where the suspects used distraction methods to get the attention of shop staff. They then stole around Â£3,750 worth of jewellery and an amount of cash. There were a group of five suspects involved, including two men and three women.
"Anyone with any information is asked to call North Yorkshire Police on 101 and pass on information to the force control room using incident reference number 12180166946. To report information remain anonymously, call Crimestoppers on 0800 555 111."