package.json only declares your app dependencies -- it tells "npm" to install some stuff when you run "npm i". When you run "npm i", it installs your dependencies to node_modules.
This is where Mojito finds them. Can you verify them this directory exists? And has async.js in it?
Armetiz, please, do not use mojito start, instead use ./node_modules/mojito/bin/mojito start from the app folder, that should solve the issue. We are in the process of fixing this in 0.5.7 with the introduction of the new pkg mojito-cli, will update this post when that gets released.