Twitter buys a company backed by...Twitter's CEO

Twitter works to improve ad targeting

Twitter just announced that it acquired an online advertising company called TellApart. Among its investors: the guy who runs Twitter.

Dick Costolo, Twitter's CEO, invested in TellApart in 2010, as part of a $4.8 million round that included Greylock Partners, LinkedIn founder Reid Hoffman and SV Angel.

Alongside the microblogging site's first-quarter earnings announcement on Tuesday, Twitter said acquiring the personalization technology gives it "additional tools for cross-device identity, targeting and attribution, along with a talented team with deep direct response expertise."

Read MoreTwitter turns to direct messaging

TellApart was founded in 2009 by Josh McFarland, a former Google executive, and raised an additional $13 million in 2011 in a financing round led by Bain Capital Ventures.

It's a fiercely competitive market that includes publicly-traded Criteo, as well as start-ups like AdRoll and SteelHouse. Ad tech has been a tough place for independent companies to scale, and Twitter has proven to be a willing acquirer after purchasing MoPub in 2013.

"Together, we're excited to bring the power of cross-device targeted advertising to Twitter, our clients and our ad exchange partners," McFarland said, in the statement.