Sign up for alerts through trade journal site or professional organizations; you can also follow them in Twitter, LinkedIn or Facebook. Library databases offer alerts but require you to create accounts first; library databases may offer full text holdings whereas the online journal's site may offer partial full-text to non-subscribers (this is called a paywall to help generate memberships or subscriptions).
From the Library:
Advertising Age In EBSCO Business Source Premier & Communication Source from 1996+ (HTML fulltext)
Adweek In ProQuest Central Essentials from 2003+ (PDF fulltext)
Advertising Age: Sign up for their daily wake-up call
Adweek: Sign up for newsletters
Learn how to set up alerts by watching this video.
When you search a database by subject, you retrieve every article in the database that contains that term in the subject field. You'll need to narrow your search by adding other key terms or limiting your search by title, date, an added subject, etc. in the left menu.