ISIS spawned from the clusterfuck which the US created in the region.
I have yet to come across a major scholar supporting ISIS. I'm a Salafi. So we are supposed to be promoting ISIS. Every single Salafi scholar has gone in lengths denouncing the ideology of the scum like ISIS. If you know of any scholar supporting them can you pls show me.
Coming to the phenomenon of youths getting enticed and joining ISIS, that is a major problem which Muslims are facing. The reasons are actually an amalgamation of multiple factors which I don't know how to express properly but I'll try.
Lack of Islamic knowledge. Most Muslims households are just culturally Muslims with a set of ritualistic practices. They might pray on Fridays or on Eids and hardly know anything about Islam apart from what the grandmother stories tell. These kids go on the internet and find some terrorist who convinces them Islam is all about blowing innocents up and they think that is what is Islam is all about and think that it is now their religious duty. If you see most of the indoctrination by these extremists happens online.
Adventure/Excitement in life.
This is a problem which almost the entire world faces. People are getting disillusioned by the travails of the modern world. It's a fact that suicide rates are increasing across demographics because people feel lost/ do not have a purpose in life. They think joining these terrorist groups will fill a gap in their lives and give them some purpose. Influence of Hollywood movies also plays a factor in increasing the "coolness" factor of these extremists. It is similar to bullies who fail in life and join the US army to kill some muzzies.
Afghanistan,Palestine,Iraq, Guantanamo Bay, Chechnya etc has made Muslims angry. When I was a teenager I came across some extremist propaganda video showing Israeli oppression. I felt so angry and wanted nothing but to go and hurt those ppl. Muslims have this feeling of Ummah which transcends nationalistic ties. We feel the pain of our brothers and sisters and want to act to help them. These extremist groups tap into that for their own twisted purposes.
Muslims are fighting an internal battle which doesn't get publicized on any news channel against these extremists. We have been holding regular youth meeting here in Chennai exposing the ideology of these extremists and making sure they aren't lead astray. It hurts to come and see on reddit people wanting to wipe out 1.6 billion people for actions of a microscopic minority.