Twitter executives have spent weeks on Wall Street and in major U.S. cities touting the company's highly anticipated initial public offering, set to take place this week. But despite their best efforts to pitch the site's profit prospects in mobile, international growth and TV integration, investors are still skeptical, results from a new AP-CNBC poll show. According to the poll, nearly half of active investors—those who had adjusted their holdings within the last year—say Twitter would not be a good investment. That sentiment is stronger from higher-income respondents; some 56 percent of those with incomes of $75,000 a year have doubts about its investment prospects. While the survey's respondents remain anonymous, some potential investors have taken to Twitter—ironically—to talk about its investment prospects.

(Read more: Twitter's mysterious outside shareholder)

"I will wait and see how the price action looks for awhile before I jump in," said Jason Whitman, a Wyoming-based optometrist who considers himself a "risk-tolerant" investor, in a Tweet.

"I will not be investing until I see how $TWTR will make a profit," tweeted Matthew Sigafus, a 35 year-old nurse practitioner from Philadelphia who invests on the side.

Conventional wisdom would say Twitter's most frequent users— which, according to an August 2013 study at Pew Research Center, are adults aged 18-29—would have the most faith in its future. The AP-CNBC study showed that to be only partly true. More than half of Americans under age 35 do think Twitter will be a success in five years, but they're not sold on investing. Fifty-two percent of respondents 18-34 said they wouldn't put their money in it. Millennials seem to be wary of buying stocks in general. In a Wells Fargo survey of 1,500 adults aged 22 to 32, more than half said they were "not very" or "not at all" confident in the stock market as a place to invest their money.

(Read more: Twitter IPO could mint more millionaires)

A similar survey by Accenture in February found 43 percent of millennial respondents considered themselves "conservative" investors. Even so, the results come amid intense focus on Twitter's nascent business model, and just days before the 7-year-old microblogging company is expected to raise more than $1 billion in its debut on the New York Stock Exchange.

Twitter CEO Dick Costolo Francois G. Durand | Getty Images

Analysts and investors alike have zeroed in on Twitter's user growth and engagement, key metrics for a not-yet-profitable company whose entire pitch is based on potential future earnings. Regulatory filings show the number of monthly active users on the site is still growing—up 39 percent in the third quarter from the prior year—albeit at a slower rate. And advertising on Twitter—which represents 89 percent of the company's revenue as of September—still relies upon users interacting with promoted content. (Read more: What's your Twitter IQ?)

But more than half of Twitter users, the poll shows, don't engage on Twitter, they just read, or "lurk." "We view Twitter's advertising solutions as somewhat unproven," wrote Scott Kessler, an analyst at S&P Capital, in a recent research report, where he also cautioned the company could harm the user experience by flooding its site with promotions.

Potential investors appear still skeptical on the sustainability of the broader social media industry, where many companies with scant earnings continue to fetch strikingly high valuations. Twitter on Monday raised the range in which it would price its offering to $23 to $25 a share, up from a previously disclosed range of $17 to $20 a share. At the high end of the new range, Twitter would raise as much as $1.75 billion and be valued as high as $13.6 billion.

Only 35 percent of the poll's respondents said that it is "extremely likely" that Twitter will be successful in the next five years. The sentiment is similar for other relatively early-stage social media platforms like Pinterest and Instagram, with less than half of Americans seeing success for those companies by 2018. Still, an October fundraising round reported by AllThingsD valued Pinterest at $3.8 billion, and Instagram inked a $1 billion deal to sell itself to Facebook in 2012. Forthcoming fundraising for Snapchat, a popular service that allows users to send messages that self-destruct, reportedly values the company at up to $4 billion. None of the companies mentioned has been profitable.

Beyond being skeptical of its viability as a public company, respondents also don't view Twitter itself as favorably as its competitors. (Read more: Twitter's sexy IPO is a trap: Trader) The survey shows just 19 percent of respondents with a favorable impression, compared to 47 percent with a favorable impression of Facebook. (And more investors had faith in Facebook as a public company, too: 54 percent of active investors say it will be successful in five years. And 54 percent of respondents at its 2012 IPO said it would be a good investment. The stock is up more than 30 percent since then.)