Twitter introduced targeted Tweets Thursday, giving brands the ability to specific audiences on Twitter without first sending a Tweet to all followers. It lets brands with different launch dates for several countries send specific custom messages at different times per country. The feature works for mobile, too. Mobile app providers wanting to reach customers on one device can do so without sending the message to desktop users. Through Promoted Tweets, advertisers only pay when users engage with the ad. Tweets that generate the most engagement are likely to appear more often.