• by Gavin O'Malley  @mp_gavin, March 11, 2016

Ready to rapidly scale its messaging business, Slack Technologies is reportedly pursing $200 million at a valuation of $4 billion.

To date, the company has already raised $340 million. The fresh funding should come together in a matter of weeks, sources tell Business Insider.  

Slack has already established itself as a company to watch in the white hot mobile messaging space. Since the spring, the start-up has more than doubled its daily active users to 2 million and nearly tripled its subscriber base to about 570,000.

Standing apart from rival messaging services -- namely Facebook -- Slack has convinced subscribers to fork over monthly fees for premium features.

Late last year, Slack Technologies started an $80 million venture fund to support the creation of apps and add-ons that complement its business-focused group-messaging service.

The fund has already invested in Awesome -- a tool that organizes Slack activity -- along with a productivity software maker and a toolkit for building chat bots.

Slack is financing more than half of the total fund, while the rest should come from its existing backers, including Accel Partners and Andreessen Horowitz.

To further encourage a complementary ecosystem, Slack is also readying the release of an app directory to show users how they can integrate apps into their chat rooms.

At last count, there were about 150 such applications.

Complicating Slack’s expansion plans, Facebook recently rolled out “Work Chat” -- a new messaging app designed specifically for business teams.

Between its WhatsApp unit and Facebook Messenger, Facebook already dominates the mobile messaging space.

But, Slack seems determined to change that. Vying for a bigger piece of the group-messaging marketplace, it recently began rolling out a conference-calling feature named Calls.

Calls has been in the works since Slack picked up Screenhero for an undisclosed sum, in January. Technically still in beta, Calls boasts some novel features, including a simple emoji-reaction system.