By Rolfe Winkler, Matt Jarzemsky and Evelyn Rusli Tech stocks have taken a pounding over the past month, putting pressure on the ecosystem for financing startups and taking them public.The market's recent downturn—despite a modest rally this week—has changed the tone in Silicon Valley and has some company directors recalibrating their expectations, said Jim Breyer, a partner at venture-capital firm Accel Partners."Not a board meeting goes by when at least half the meeting isn't spent on financial strategy," said Mr. Breyer, who also is chief executive of Breyer Capital. "That might have been 25% of the board meeting six months ago and a much quicker and more conclusive discussion."The next big test will come with Weibo Corp., the Twitter of China, which begins trading Thursday on the Nasdaq Stock Market. Late Wednesday, Weibo set its IPO price at $17 a share, at the bottom of the projected range of $17 to $19, and trimmed its offering to 16.8 million shares, fewer than the 20 million expected. The tech-heavy Nasdaq Composite Index was down 6.5% from its March peak as of Wednesday's close. Popular consumer Internet companies are off much more. Facebook Inc. on Wednesday finished 17% below its record close and Twitter Inc. was down 39%. Companies specializing in cloud computing, a sexy side of the tech universe these days, also are off substantially, led by Workday Inc., down 33% from its high, and ServiceNow Inc., down 26%.The result is a growing caution among some investors to buy into companies that might be struggling to show sufficient profits to justify their lofty private-market valuations.That may not bode well for companies like Box Inc., the digital-storage specialist, which is expected to start a roadshow for its initial public offering soon but that has logged significant losses. Box declined to comment, citing the quiet period before its IPO."We're obviously in the throes of what feels like a correction for the small-cap and growth-equity companies," said David Golden, managing partner at Revolution Ventures, which is based in San Francisco. A company in Revolution's portfolio went public last month and has fallen short of expectations, he said. "We were expecting the proverbial aftermarket pop, and instead it's trading at the offer price."The selloff has spelled trouble for several recent tech IPOs. The offering price on Monday of cloud-based payroll-software maker Paycom Software Inc. was well below its forecast, after failing to price the deal as scheduled last week. Globoforce Group PLC, which makes software that employers use to track workers' evaluations of each other, last month shelved its IPO plans."We all feel like we're at the top of the cycle, and everyone's skating on new ice," said Nick Beim, partner at venture-capital firm Venrock. "Just how thin the ice is not yet clear."Investors also have been less willing to take a leap of faith on uncertain businesses. Shares of King Digital Entertainment PLC slid 16% in their March debut. It was the worst first-day performance of any new listing this year as some fund managers said the company will be hard-pressed to replicate the success of its "Candy Crush Saga" mobile game.As for private financing, Michael Moe of GSV Capital Corp. predicted that market conditions would have at least some moderating effect on what have been soaring valuations."I think prices will get more favorable for buyers because it will be more difficult to do megadeals at megavaluations" until the markets pick up steam, he said.Some of the firms that have been the most active in late-stage private fundraising have been burned by the public market. Hedge fund Coatue Management, which backed ride-sharing service Lyft Inc. and photo-sharing platform Snapchat Inc., said this month that it would return $2 billion to investors from its flagship fund after taking losses in March.Some deals are still getting done and investors have found several compelling offerings. Shares of takeout ordering platform GrubHub Inc. and advertising-technology company Rubicon Project Inc. have rallied since their IPOs earlier this month.Through Tuesday, just two tech or Internet company IPOs this year had priced below expectations, according to Dealogic, Paycom and Five9 Inc., which makes software for managing customer support. And shares of tech and Internet companies that went public this year were up an average of 12% from their offer prices through Tuesday, according to Dealogic, outperforming many broad stock indexes.Still, the recent turn in investor demand for tech stocks illustrates how quickly the market environment can sour, catching companies off guard as they prepare IPOs. The blockbuster returns generated by some of last year's best-received tech IPOs have fizzled. Shares of 3-D printer maker Voxeljet AG, health-care software maker Veeva Systems Inc. and employee-benefits software provider Benefitfocus Inc. all popped in their trading debuts last year. But in each case, the shares were down more than 50% from their post-IPO highs through Wednesday.Venture capitalist Bill Gurley, a partner at Benchmark, said part of the blame lies with his industry. "You have seen an increasing amount of risk-taking by venture capitalists, pushing companies out that are further and further away from profitability.""I think these experimental IPOs will struggle in this environment," he said.For now, concerns over market volatility are likely highest among people involved with companies planning to go public in the near future, said Lise Buyer, principal at Class V Group, which advises companies through the IPO process.Sabre Corp., the parent of the Travelocity website, on Wednesday priced its IPO below expectations. Also in the tech IPO pipeline: Zendesk Inc., which provides Internet-based customer-service software; TubeMogul Inc., which specializes in online video advertising technology; and Mobile Iron Inc., which provides security for mobile apps."Those companies midstream [in the IPO process] are full-speed ahead, recognizing that whatever the market does in mid-April, may or may not have any impact on companies focused on a mid-May" debut or later, Ms. Buyer said. "If the downturn persists for six weeks or perhaps months, we may see a valuation impact. But those investing, even late-stage, in private companies are generally focused on where the market will be in six months or a year, not the next six days or a week." Corrections & Amplifications Shares of King Digital Entertainment PLC slid 16% in their March debut. An earlier version of this article incorrectly said they slid 6%. Write to Rolfe Winkler at rolfe.winkler@wsj.com, Matt Jarzemsky at matthew.jarzemsky@wsj.com and Evelyn Rusli at evelyn.rusli@wsj.com