SQL Replication Automatically Add table to Publisher
There is no inbuilt way of automatically adding new table to replication. This means, you have to carve out your own method suited to your environment.

Couple of thing that you should do ..


Poll sys.tables or have a trigger to fire on CREATE_TABLE 
Check if table has primary key (must for replication)
modify publication property - immediate_sync to 0 --> should be done once to avoid generating snapshot for all articles.
Call sp_addarticle and sp_addsubscription to add article to publication and subscription. 
Kick off snapshot .. this will generate ONLY shapshot for the article that is newly added.