A further 80% also felt that Americans should be concerned about government surveillance, Pew Research suggested.
It looked at attitudes to privacy and data in the wake of Edward Snowden's allegations about government snooping.
One expert described the findings as "unsurprising".
The high level of media attention given both to the Snowden allegations and to large-scale data breaches among well-known US brands means concerns about privacy are at an all-time high, according to report author Mary Madden.
"There is both widespread concern about government surveillance among the American public and a lack of confidence in the security of core communications channels," she said.
"At the same time, there's an overwhelming sense that consumers have lost control over the way their personal information is collected and used by companies."
Since contractor Edward Snowden began leaking details of the surveillance programs used by the US National Security Agency (NSA) and the British intelligence agency GCHQ, firms have sought to reassure customers that their personal data is safe.
Some, including Microsoft, Yahoo, Apple and Google, have promised higher levels of encryption for personal data to make it harder for governments to snoop.Delicate balance There is very low confidence in the way firms handle data, according to the survey
The survey suggested that most customers remained suspicious of how companies used their data.
Some 80% of respondents who use social networking sites said that they were concerned about third parties such as advertisers or businesses accessing their online data.
Fewer, although still a significant number - 70% - were concerned about the government accessing the information they shared on these sites.
Large numbers - 64% - said that it was up to government to regulate the way advertisers accessed data.
Consumers indicated that they were pretty savvy about the delicate balance between privacy and access to services.
More than half (55%) agreed that they needed to share information about themselves in order to have free use of online services.
But the majority (61%) were not buying the idea that online services were made more efficient because of the increased access they had to personal data.
When asked what communication medium respondents felt was the most secure, the winner was the landline phone - although only 16% said they felt "very secure" using it to share private information with another trusted person or organisation.
Social media sites were regarded as the least secure, with only 2% saying they felt "very secure" using such services.
"People's perceptions of privacy are varied but there are universally low levels of confidence in the security of communication channels," said Ms Madden.
The survey, which recorded responses from more than 600 people, is taking place over the course of a year to chart changing attitudes to privacy.
The next survey, due next month, will look specifically at attitudes to how information is stored and secured and the following one will focus on behavioural changes in the post-Snowden world.
There is already evidence that people are considering changing the way they secure their personal information, with 61% claiming they would want higher levels of protection for their data.
"People aspire to do more - to use encryption or other tools to secure their information," said Ms Madden.
Security expert Bruce Schneier said that the survey results were "unsurprising".
"We know that people are concerned about privacy but we also know that they don't think about it when they are sharing data on Facebook because we have to socialise," he said.
"People give Google their data and share on Facebook. Surveillance is the business model of the internet. Google knows more about what you think about than any other company on Earth."
He is also sceptical that people will turn to technology to solve the problem.
"People want legislative change rather than technology tools. People tend to do what is easy."