Jeremy Stoppelman, CEO of Yelp.com, a business and consumer review website, pose during a visit to New York, Tuesday Feb. 24, 2009. Yelp.com, based in San Francisco, relies on users to create its content with reviews of everything from A to Z.

San Jose, Calif. ? Yelp.com prides itself on being a site where people can write reviews about pretty much anything and connect with similarly critical peers. Yet as the site grows, some of the businesses scrutinized on Yelp are turning the tables and griping about the company itself.

The complaints highlight an irony for Web sites that stimulate online communities and let users speak their minds. As the sites make the world more transparent, giving people the power to discuss everything from a great pizza to a bad date, the sites’ own transparency is often questionable, as consumers and businesses struggle to understand how they operate.

This tug of war has become increasingly public with the explosive popularity of social Web sites like Facebook, Twitter and MySpace, as well as niche sites like Yelp, which has more than 5 million reviews on establishments in dozens of cities.

Properly balancing the interests of various constituencies — and retaining their loyalty, perhaps through improved channels of communications — will prove key to whether the sites can grow into vibrant, moneymaking operations for years to come.

Many sites have expanded so fast that explanations about what they are doing often come late — after their users have had plenty of time to air complaints. Facebook has felt such growing pains, and now Yelp is, too.

One big gripe from businesses that get reviewed on Yelp is that they don’t quite get how it works.

For instance, some wonder why users’ reviews can seemingly mysteriously disappear from Yelp’s pages about a business.

This irks Leslie Tagorda, owner of a San Francisco-based Web design company, Flair-Designs. She has noticed reviews vanish from the Flair-Designs page on Yelp over the past two years. This worries her because the more reviews she has, the more calls she gets from potential clients, she said.

When she first noticed reviews disappearing, Tagorda contacted clients who had written the comments, to see whether they had deleted them. They said they had not.

She e-mailed Yelp and was directed to the business owners’ section of the site. Not satisfied, she aired her issues by writing a review of Yelp itself on Yelp’s business page, giving the site two out of a possible five stars.

At last she got a more personal message from Yelp’s chief executive and co-founder, Jeremy Stoppelman. He explained that consumer reviews may be removed by an automated program that is designed to filter out reviews the site considers untrustworthy, such as sniping that a pizzeria owner might write about a competitor.

Tagorda was satisfied with Stoppelman’s response but still wanted people to see what she felt were legitimate reviews that Yelp had hidden. So Tagorda put up a post on Yelp about her own business, indicating the names of users whose Flair-Designs reviews have disappeared. If you search for those users, you might be able to find their reviews of Flair-Designs under their personal profiles.

So far, her post about Yelp has stayed up, and she recently added a star to that review, updating it to say she’s “becoming a little happier with Yelp as a business owner.” Still, the whole episode has her feeling murky about the site.

Stoppelman acknowledges that the fluctuation of the site’s reviews “flusters and surprises a lot of business owners.” Some explanations are in the site’s “frequently asked questions,” but not everyone reads those.

However, Stoppelman believes there will always be tension between Yelp and business owners because consumers are creating the content, which is inherently unpredictable.

Yelp is not the only social site grappling with transparency.

Facebook tackled it most recently after thousands of its more than 175 million users protested a quietly made policy change that appeared to let Facebook gain more control of photos, messages and other information that people share on the site.

Facebook Chief Executive Mark Zuckerberg responded by assuring users that they, not Facebook, own their content. The site also decided to let users play a “meaningful role” in determining shifts in Facebook’s policies.