Wind Rider by Teddy Jacobs

This is the second book in the Return of the Dragons series.

Wind Rider continues the story of Anders Tomason, a 16yo boy who has recently learned he is the prophesied Three Bloods Prince, and it is up to him to beat The Dark Lord, who happens to be his uncle!

The blurb says:

Anders Tomas (sic) already found a magic sword and clashed with his evil uncle in SWORD BEARER. Now he returns in this second adventure, and continues his struggle with the evil chemical forces that threaten his world, enlisting, in the process, the help of the dragons.

 Again, this book is fast based so adult readers may not find it has enough depth to keep their interest.  However, reading it as aimed for teens, the story has a good pace and keeps you wanting more.

Unfortunately, two books is not much of a series (not to mention that the series is entitled Return of the Dragons - which only appear halfway through the second book) and as this book was published back in 2012, it looks unlikely that there will be a third book any time soon.  As such, the ending is a bit swift, and though Anders wins a battle in this book, it is clear that he hasn't won the war. 
I cannot find much out about the author - for example his website was updated in 2013 - so I hope he's ok. 

One way you could get enjoyment from how this ends, however, is if you use it as an opportunity to encourage your teen/preteen to do some creative writing themselves and to finish the story themselves.