Good morning all ! I hope you're okay ! I've seen a lot of Ravenclaw and other students also wonder how Voldemort found the Ravenclaw diadem. So today I am writing this article for all of these people.

Well I watched a video on YouTube explaining this theory. So let's get started!

Helena Ravenclaw, daughter of Rowena Ravenclaw, was very jealous of her mother because she was famous and very intelligent. For this, she stole her diadem and fled Scotland, Albania.

When Rowena fell ill, she asked Bloody Baron, who loved Helena, to bring her daughter back. The Slytherin ghost found her but she didn't want to go back to her dying mother. Bloody Baron put the girl to death. After that, he too gave himself up to death.

Tom Riddle, knowing this story, had enough data for Helena’s character . Firstly, Voldemort got closer to the Grey Lady and he told her things about him, to show that he liked her and earned her trust. So, the moment that Helena will fully trust him, he will talk to her about the diadem and how her life would be much better if he would destroy it. 

Through this "game", Tom Riddle would indirectly force the Grey Lady to think that he could help her get rid of the magical object that contributed to her personal destruction, reaching practically the point of begging him to take over this obligation towards her and necessarily reveal to him the whereabouts of the diadem. 

Source : https://www.youtube.com/watch?v=eFZ2pbnbvf0

Claire Angelina Herkins , HDN Writer