The Slack app logo is seen on a smartphone in this picture illustration taken September 15, 2017. REUTERS/Dado Ruvic/Illustration

(Reuters) - Slack Technologies Inc, a provider of chat and direct messaging services for businesses, has hired investment bank Goldman Sachs Group Inc GS.N to lead its initial public offering (IPO) next year as an underwriter, people familiar with the matter said.

The San Francisco-based company is among a string of Silicon Valley unicorns expected to debut in the stock market in 2019. Other IPO hopefuls include apartment-rental service Airbnb Inc, analytics firm Palantir Technologies and Stripe Inc, a digital payment company.

Ride-hailing company Lyft Inc beat bigger rival Uber Technologies Inc in filing for an IPO this week, defying the recent market jitters that have weighed on corporate valuations.

Slack is rounding up its underwriting syndicate and hopes to fetch a valuation of well over $10 billion in its IPO, whose exact timing will depend on market conditions, the sources said on Friday.

The sources asked not to be identified because the matter is confidential. Slack and Goldman Sachs both declined to comment.

Slack is competing against the likes of Microsoft Corp's MSFT.O Teams, Alphabet Inc's GOOGL.O Google Hangouts Chat and Cisco Systems Inc's CSCO.O Webex Teams in the so-called workplace collaboration market, which research firm IDC has projected will be worth $3.2 billion by 2021.

Slack last raised $427 million in August in a private fundraising round, led by Dragoneer Investment Group and General Atlantic, giving it a valuation of more than $7.1 billion. It previously raised $250 million in 2017 at a $5.1 billion valuation, in a fundraising round led by Japan's SoftBank Group Corp 9984.T.

It is unclear how market turmoil fueled by the escalating trade tensions between the United States and China could impact Slack’s IPO plans.

On Thursday, biotechnology company Moderna Inc MRNA.O braved market volatility and sold around $604.3 million in shares in its IPO.