Slack Technologies, the US-based messaging app developer backed by internet technology group Alphabet, is looking to raise another $150m, the Wall Street Journal reported on Tuesday.
The company is in the process of approaching prospective investors and is seeking a higher valuation than the $2.8bn valuation at which it raised $160m in April 2015, a person familiar with the matter told the WSJ.
Slack started out as a game developer called Tiny Speck in 2009 before pivoting to concentrate on its workplace messaging software.
The company has reportedly more than quadrupled its user base from 500,000 to 2.3m million daily users in the past year and estimates its annual recurring revenue is more than $64m, but it has also been burning money, expanding its workforce from 103 to 369 people and running TV advertising spots.
Slack has raised more than $340m in venture funding since 2009, with Alphabet subsidiary Google Ventures co-leading a $120m series D round with Kleiner Perkins Caufield & Byers in late 2014 that valued it at $1.1bn.
Google Ventures, now called GV, returned for a $160m series E that closed in April, and which also included Horizons Ventures, DST Global, Index Ventures, Spark Capital Growth and Institutional Venture Partners.
Other investors in Slack include Andreessen Horowitz, Accel Partners and The Social+Capital Partnership, all of which took part in the series D round as well as a $42.8m round that closed in spring 2014.