[Lothiriel Silmarien]

Well, I was planning to give a really good answer, but a couple people beat me to it! But maybe Fingon didn't involve himself more because he wasn't as close to Morgoth's territory as Maedhros was, and he felt that Morgoth's armies wouldn't reach him fast since his land was pretty much surrounded by mountains. That still doesn't say much though because Maedhros and Fingon were friends.

I'm not sure if that was a question about why Thingol didn't involve himself, but he wouldn't of anyway because of his grudge against the Noldor for the kin-slaying and he wasn't particulary fond of the sons of Feanor. Besides from the obvious, he felt that the others should take care of it because all of the bad things that started happening came from the return of the Noldor. He also felt that his region was safely protected by the Guard of Melian, so that's another added reason.