As the boy stewed in his cell he realized that there was a way out. But that wouldn't come easily. He had to learn magic. Plotting how to escape the boy asked the nearby slaves what they knew about it. After asking every slave he saw for a week he managed to figure out that you couldn't just use magic you needed to route how the mana flows through your body. While it sounds easy you need lots of money, time, and resources which were all things the boy didn't have.
With magic off the table he needed a different way out. As the boy was thinking a slaver came up to him and in a satisfied voice said.
"You were just bought so you're not our problem anymore". He had been sold? That means all the disappearing slaves were also sold.
"You'll be leaving tomorrow" said the slaver. The boy nodded.