Yelp allows the multitudes to fancy themselves restaurant critics, Twitter gives them an outlet to celebrate the perfect pizza or slam the worst Key lime pie ever, and Foursquare lets friends track one another's every move. Now, along comes a flurry of start-ups that use social media tools to help foodies follow one another's eating odysseys on the Web, where 600,000 or so food-blog listings are already found on Google. No one has yet figured out how to turn these businesses into moneymakers. For those who do, the payoff could be sweet.

Foodspotting
When Foodspotting launched early in 2010, it was dubbed "the Foursquare for food." Foodies use a free iPhone app to photograph restaurant dishes, and, as with Foursquare, they earn points and badges for contributing tips that prove popular with other Foodspotting users. Photographs are searchable by restaurant, type of dish, and location. Founders Ted Grubb, Alexa Andrzejewski, and Soraya Darabi hope to make money by selling advertising within search results. Another income source could be guides sponsored by media companies that would offer prizes for, say, sampling the most items posted on Foodspotting. The San Francisco Chronicle has launched a beta guide on the site.
USERS: 140,000

Fiddme
A Twitter posting by Yosi Taguri, one of four Fiddme co-founders, on the "best mille-feuille pastry ever," which he tasted while in Paris, led to an enthusiastic string of responses and, soon thereafter, the creation of the Fiddme site. The Israel-based start-up focuses on building foodie communities. Whenever users update their Fiddme accounts, their Twitter, Facebook, and Foursquare accounts are also updated. Friends can follow one another's restaurant outings and browse photos and descriptions of meals their friends have posted. Fiddme also encourages cooks to post recipes and photos of their personal creations for comments.
USERS: 30,000

Eat.ly
Four friends in New York City and London figured that if they could remember what they ate, they would eat more healthfully. So, in November 2009, Sam Huleatt, Mike Singleton, Eric Friedman, and Sam Brown teamed up to created Eat.ly, a website on which users can post photos of their meals and track their eating habits by assigning the photos health rankings. Profiles can be made public, integrated with Twitter and Foursquare, or remain private for a defined group of friends or to share only with, say, a trainer or nutritionist. The founders plan to earn income by selling their software platform to people who want to create similar sites on different topics.
USERS: 3,000

Chevia
Its Foodstream app tracks local food news. Users get a news feed of local posts that might include restaurant specials or new dishes. Founder Paul Lo, a former Yahoo software developer and executive, hopes to make money from advertisers, which will be able to place their spots based on user preferences. Advertisers can target their messages to audiences based on geographic area or what sorts of foods or restaurants they indicate they enjoy. Lo also envisions businesses paying to sponsor contests that award prizes for, say, the most tacos eaten outside the U.S. or the most pizzas consumed in Chicago. The site launched recently; a beta version was well received.
USERS: 1,000 (beta version)

THE LINE: Foodspotting has amassed the largest user base, but its success depends heavily upon advertisers' willingness to pay for preferential positioning on the site. Chevia is in a similar situation. Eat.ly has the advantage of serving two vast markets — foodies and weight watchers. But Foodspotting's interactive guides and Chevia's business-sponsored awards may be the fastest ways to bring in revenue.