One of my company's users doesn't have a follow button in the Sharepoint ribbon (Office 365). All other users do have this button. Is there an individual setting in Sharepoint that might be the cause? The overall site settings state that the follow functionality is enabled.
You need to setup onedrive by clicking on it from the app launcher. Once that is setup, the follow icon would start appearing on the site as well as documents. This[one drive setup] needs to be done by each user on the tenant.
If you don't see OneDrive, it could be you have an Exchange Online Plan 1 license. While SharePoint is functional, certain features are unavailable. This also impacts the SharePoint and OneDrive mobile apps.