In its continuing quest to prove to investors that it will be an advertising powerhouse, Twitter announced Monday that it had acquired an ad-tech startup and launched the ability to more powerfully promote mobile applications on its service.

The San Francisco social-networking company confirmed the acquisition of TapCommerce, a New York startup that focuses on "retargeting" -- contacting customers who have expressed an interest in purchasing something online in an attempt to close the deal.

"Advertisers spend aggressively to get new users, but re-activating existing or previous users can provide just as attractive a return on investment," Twitter's vice president of global online sales, Richard Alfonsi, said in the company's blog post on the acquisition.

Twitter did not release a purchase price for the acquisition, though Recode reported the deal was for about $100 million in breaking the news before it was announced, and Bloomberg News later reported the same figure; both reports cited an anonymous source. That purchase price is larger than most Twitter acquisitions, which typically focus on acquiring engineering talent or specific functions, but pales in comparison to the $350 million purchase of ad-tech company MoPub, Twitter's largest acquisition to date and the core of its advertising offering.

"It's another step in this bigger vision we've started to put together about mobile advertising," Alfonsi told Bloomberg in an interview on the subject.

Earlier in the day, Twitter announced another aspect of its vision with the official rollout of ads that allow users to install mobile applications, an advertising concept that proved profitable for Facebook and could leverage Twitter's large audience of mobile users. Twitter began testing ads that allow users to instantly begin installing a mobile app in April, and companies such as ride-sharing app Lyft and video-game giant Electronic Arts praised the offering in Twitter's blog post on the official rollout Monday.

"We were able to drive a significant number of installs for our suite of casual and core games," Uyen Uyen Ton Nu, senior manager for social acquisition at Redwood City-based EA, said in the blog post.

Twitter sold shares at $26 apiece in a 2013 initial public offering and shot higher in the first few months of the stock's availability, but slowing user growth has hurt the company's market capitalization of late. Shares gained 0.1 percent to $40.97 Monday, and increased 26.3 percent in the month of June, but that price is still 45 percent lower than Twitter's all-time intraday high of $74.73.