Dara Khosrowshahi, chief executive officer of Uber Technologies Inc., listens during a panel discussion at the Bloomberg Global Business Forum in New York, U.S., on Wednesday, Sept. 26, 2018.

Shares of Uber continued to sink on Monday, posting their lowest close ever, after the company reported disappointing second-quarter results last week.

The stock dropped 7.6% to $37.00, falling below its previous low of $37.10 on May 13. Since its debut on the public markets in May, Uber shares have shed about 18% of their value from the company's IPO price of $45 per share.

Uber posted a staggering $5.2 billion loss in its latest quarterly results, driven primarily by stock-based compensation costs. The company reported a per-share loss of $4.72 on revenue of $3.17 billion, both of which missed analysts' estimates.

In an interview with CNBC's "Squawk on the Street" on Friday, CEO Dara Khosrowshahi characterized the losses as a "once-in-a-lifetime" hit as he tries to steer the company toward profitability.

Investors continue to remain skeptical about whether or not Uber can achieve profitability in the future. Those concerns have put Uber and rival ride-hailing firm Lyft's shares under pressure in the months since their respective IPOs. Shares of Lyft fell 4.9% on Monday.

Early Uber investor Bradley Tusk told CNBC on Monday that the company needs to dominate in more areas than just Uber Eats and ride-hailing in order to become profitable.

"They've got to be that A-to-Z for transportation," Tusk said. "Whether you're getting yourself to A-to-B on a bike, scooter, or a car, bus, whether furniture being shipped on a truck, or a burrito from a messenger, they've got to be the default for all of that."

Correction: This story has been updated with the correct percentage fall of Uber's stock from IPO price.