And the "composer install" succeeded without errors?
If so, you should now have a ./fuel/vendor/autoload.php file and a ./fuel/vendor/composer folder. If not, something went wrong with running composer.
If you have the files, you haven't set up your project file and folder rights properly, which causes files you create on the commandline not to be readable by your website user. So check your permissions.
I use a special "www" group, of which both my webserver user and my commandline user is a member. And I use this in the project root:
chgrp www -R
find . -type d -exec chmod 2775 {} \;
find . -type f -exec chmod 2664 {} \;
This will make the group sticky, so it also works for new files and directories. For production sites, you might want to reduce the group and world rights in the projects public folder.