The startup world can be a volatile one. The sudden shutdown of Las Vegas-based virtual assistant service Zirtual is a reminder that things can go south, apparently in an instant.

Zirtual's clients and about 400 employees received an e-mail today that said the company would immediately be halting operations due to “market circumstances and financial constraints." Zirtual deleted its Twitter feed, Facebook page and Google+ account. As of now, there is no farewell post on its corporate blog. The full letter is included below.

Related: How to Shut Down Your Struggling Startup

The company allowed clients to employ a dedicated virtual assistant to handle tasks like scheduling, billing, booking travel and more. It was founded in 2011 by CEO Maren Kate Donovan, head of UX Erik Jensen and head of people and culture Collin Vine. Ramon Icasiano, who has worked for Netflix and Verizon, was hired as COO in May.

From the outside world, nothing seemed amiss. Zirtual secured $2.6 million in debt financing in June and an additional $650,000 at the end of July and counted Zappos founder Tony Hsieh as one of its early investors. In April, the company released a statement highlighting the fact that its workforce was made up of full-time employees with benefits, rather than contractors.

Related: How to Save Your Business From Doom

Donovan's last tweet was posted on Saturday, in which she thanked angel investor Jason Calacanis – who also invested in the company -- for having her on his podcast, This Week in Startups. During the hour-long conversation posted on Friday, Donovan did not discuss that the business would be closing its doors.

The abrupt nature of the company's shutdown and has led to a less than favorable response on social media, but it seems that some former clients and their assistants are planning to continue to work together.

Related: 5 Truths to Remember When Facing Failure as an Entrepreneur

Dear Zirtual Clients,

It is with an incredibly heavy heart that I have to send this message. As of today, August 10th 2015, Zirtual is pausing all operations.

Due to a combination of market circumstances and financial constraints we must re-organize our current structure if we are to successfully serve you in the future.

I realize this news comes incredibly fast and I am truly sorry for the Z-shaped hole this will leave in your lives and business.

We know that many of you care deeply about your Zirtual Assistants. If you would like to connect with your assistant independently, please reach out to: questions@zirtual.com.

Thank you from the very bottom of my heart for the support you’ve shown Zirtual and my deepest apologies for the speed and inconvenience of this announcement.

We will communicate any further updates as soon as we have them.

Best, Maren, Erik, Collin + the Zirtual Team