Twitter announced Monday that it has cut a deal to buy mobile ad firm Tap Commerce to bolster money-making tools at the popular one-to-many messaging service. San Francisco-based Twitter did not disclose how much it paid for Tap Commerce, which is located in New York City, but technology news website Recode.net reported the deal to be valued around $100 million. Advertisers spend aggressively to get new users, but re-activating existing or previous users can provide just as attractive a return on investment, Twitter said in a blog post about the Tap Commerce acquisition. Together with the Tap Commerce team, Twitter will be able to offer mobile app marketers more robust capabilities for app re-engagement, tools and managed service solutions for real-time programmatic buying, and better measurement capabilities.