As you know, SharePoint Online came with an initial enterprise social feature called Newsfeed.
This is (used to be) the default social feature on SharePoint Online but you were able to switch to Yammer.
In June 2018, the Newsfeed will be set to read only for existing tenant and will be removed for new tenant.
This will ultimately leads to a removal of the feature for existing tenant.
You should consider moving to either Yammer or Teams/Communication sites.