Of course he should be punished. Sorry, but he's gone out of his way to look for girls that are thirteen, despite the copious amounts of hot 18 year olds available. At 13 I took whatever I could get. I had like an old early 90's mag (it was pretty awful), and that did me just fine. In fact, it was pretty incredible at the time. This kid is showing serious INTENT by purposefully looking for underage girls online. Besides that, in this country, it is Illegal to view ANY porn under 18. So he's breaking the law. Full stop.
However, he would be tried as minor, and should not be put on a sex offenders register or anything like that. I'm not sure under 18's even can be put on a sex offenders register, unless they do something REALLY serious, like rape. Even then, I'm not sure on the protocol.
The person who took the images and hosted them should be punished worse. In this day and age, it seems stupid that we can't track the sources of this abuse.