Young means different things to different people... Neymar is young, doesn't mean you can or should sign him. Without more information, it's a bit hard to help. What's your budget, where do you want him to play (1st team, etc.), what kind of striker do you want (TM or Treq)?
If your definition of young is the same as mine (U18)... Take a look at Belgian striker Siebe Schrijvers, Finnish youngster Joel Pohjanpalo, English speedster who plays for Derby Mason Bennett, Spanish future star Paco Alcacer, or if you really want a cheap youngster scout out Norwegian Bard Finne.
Just a few off the top of my noggin that can turn out pretty solid with a couple years of training, but few of them are ready for full time 1st team action.
If you're looking for immediate impact, look to the usual suspects... Abel Hernandez, Vaclav Kadlec (if you need cheap), or if you want to put in a little effort Carlos Fierro and the other young striker from Chivas in Mexico, Erick Torres, are still solid choices. Mattia Destro is also a solid "young" choice, and can be gotten for free in the middle/end of the first season.