This article covers the SFDC table which stores Chatter Follower information (ie It stores which user follows which Account, Contact , or any record or User).

The table is

EntitySubscription:

The fields in this table are

ParentId:              The ID of the Account, Contact or any record or User.

SubscriberId:      The ID of the user who follows the record denoted in the Parent ID.


Querying this object would give you Follower Information

For Example:

List<EntitySubscription> myaccsubscribers = [Select ParentId,SubscriberId 
from EntitySubscription where ParentId = '500Q11100046Vt3']; 

To Add followers automatically using Apex, you could insert records into this object. And to Un-follow just delete the relevant records.

EntitySubscription newfollower = new EntitySubscription();
newfollower.ParentId = 'insert id here';
newfollower.SubscriberId = 'insert the user id here';
insert newfollower;