This is a stupid question. On YouTube I have seen all these people who mix songs such awesome songs which I have never heard of. So my question is how do they find these song? I mean what do I search for on the internet?

Music isn't something that you search for, because we don't use YouTube or SoundCloud thinking, "Hey let me hear a bunch of songs that I haven't heard" No, We come across music in many different ways such as, We listen a song in an Advertisement, in a movie as a soundtrack, sometimes on radio, or when someone else is playing etc etc. Then we search for it. It's the hardest thing to do. 1) You type all the words from lyrics you remember & google it & hope for the best. 2) Or use apps like Shazam & SoundHound. When you finally find the song you're looking for, you look around for similar songs from the same genre & artist or others. Since we go through all the trouble finding this song it pretty much means that you liked it & you're hooked to it. Atleast that's how I discover new music.

Channels like- Mr Suicide Sheep, The Sound you Need, Soundowl. Once you subscribe some channels like these, you will be shown similar channels by youtube itself