I faced this problem many times but got no where. But I did come up with a solution(for me it worked).
I found out(for me) I had a runtime error. What this is that construct 2 does export you game(s) to Windows,Mac,Linux, but the runtime is messed up. So here is what I did to have my mac game running on Yosemite(the one I used)
1. Go to nwjs and get the mac version of nwjs(not windows)
NOTE: when you do get the mac version of nwjs, don't download the SDK version. That lead me to no where
2.unzip the nwjs for mac and put the folder somewhere in desktop screen(home screen when you log in to mac)
3. then what i did was open the folder, and found the exact icon as my exported game from Construct 2.
When I opened it, I saw a NW.js screen,then exited out of the app.
4.Then what I did was right click thee nwjs.app(not the newproject.app) and clicked on Show Package Contents.
5. Then what I did was, I went back to my exported game: newproject.app(when I exported the game, this is what I saw as the title.), and right clicked on my game and show package contents.
6. Now what I did was,I moved the files from the nwjs.app(again, not the newproject.app).
I moved: Macos, Versions, Info.plist, and PkgInfo.
NOTE: I did not select Resources folder.
7. Now what I did was, I went back to my newproject.app(not nwjs.app) and right clicked on the app and selected show package contents. Once selected, I open the Contents folder, and saw the exact same thing as nwjs.app had.
8. Now I had 2 folders open( one nwjs.app and one newproject.app) and copied the Macos, Versions, Info.plist, PkInfo to the contents folder of newproject.app.
It also asked me to replace the same folders/files so i clicked on replace. Assuming I did not copy the Resources folder to the newproject.app/contents folder
9.Once I moved those files/folders to newproject.app/contents folder, I exited out both folders(newproject.app and nwjs.app). Then clicked on newproject.app and saw my game running.