You’ve read all of your free items this month. To register, get added benefits and unlimited access to articles, Become a Member. Already a Member? Sign in. Advertising Age Article Abstract Twitter Opens Up Self-Serve Ad Platform to 10,000 Small Businesses American Express Cardmembers and Merchants Eligible to Register for Platform Starting Tonight By Cotton Delo, Published on February 16, 2012 3 Want more Access, Content & Connections? Upgrade to Membership. We are glad you are enjoying Advertising Age. To get uninterrupted access and additional benefits, become a member today. Become a Member Already a member? Log in.