Twitter, the micro-blogging system that was one of the last ad-free spaces on the Internet,

announced Tuesday that it would start selling advertising.

Companies will be able to pay to have their ads appear at the top of Twitter search

results, part of the site&#8217s attempt to begin profiting off its millions of users.

The ads became a hot topic on &#8212 of course &#8212 Twitter and tech blogs, and local

denizens said they trust Twitter to take the right approach in introducing advertising to the

site.

&#8220I guess that I&#8217m not thinking Twitter is going to beat us over the head with

ads,&#8221 said Keith Burtis, a social and digital media consultant and well-connected Twitter

user in Amherst. &#8220I&#8217ve seen grumbling already, but it&#8217s from people who are

going to grumble no matter what.&#8221

Twitter&#8217s users send &#8220tweets&#8221 of up to 140 characters that can range from

the profound to the mundane, with an emphasis on what someone is thinking or doing at that

moment.

The site has soared in popularity since its launch in 2006, but it has come under pressure

to wring revenue from its users.

About 69 million people worldwide used Twitter.com last month, up from roughly 4 million at

the end of 2008, according to comScore Inc.

&#8220Everyone knew they were searching for a way to make money,&#8221 said Adrian Dayton,

a local attorney and author who advises major law firms on how to use social media.

In a blog post Tuesday, company co-founder Biz Stone said the company took its time

&#8220because we wanted to optimize for value before profit.&#8221

Users will see the &#8220Promoted Tweets&#8221 when they search Twitter for what everyone

else is saying about the hot topics of the day, just as targeted ads show up on Google and

other search engines.

Many companies have Twitter accounts already, but tweets they send out can get buried in

the massive and constantly updated stream of tweets referring to the company by name.

Twitter named Virgin Airlines, Best Buy Co., Sony Pictures and Starbucks Corp. among the

other companies using Promoted Tweets in tests.

The ads will be rolled out gradually, with fewer than 10 percent of Twitter&#8217s users

likely to see them at first.

The company says the ads should be appearing in all relevant searches within the next few

days. Promoted Tweets will be identified as such in small type.

Twitter&#8217s Stone said Promoted Tweets will need to resonate with users. If a Promoted

Tweet isn&#8217t replied to or forwarded by other users, it will disappear.

Burtis, who uses Twitter extensively to promote his business and connect with people, said

he doesn&#8217t mind the site adopting an ad-based revenue model.

&#8220I&#8217d like to see this service stick around,&#8221 said Burtis, who called Twitter

&#8220transformative.&#8221

Even though he would be willing to pay to use Twitter, he knows other users would not.

&#8220If they went to the &#8216pay for&#8217 model, I think they would immediately stunt

their growth,&#8221 Burtis said.

These ads could be helpful.

Dayton used Twitter to ask his more than 50,000 followers which smart phone he should buy.

The iPhone, BlackBerry and Palm Pre all received tweets of support.

Dayton said he wouldn&#8217t have minded if phone makers had responded to his question with

useful information in an ad.

&#8220I would be fine getting sponsored answers,&#8221 said Dayton, who bought a Palm Pre.

There is at least one wrinkle with the Twitter ad plan, however: Many users don&#8217t

connect with the service through searches or visits to the site.

Instead, they use mobile and desktop software applications with names such as TweetDeck and

UberTwitter.

Recognizing this, Twitter said it might take Promoted Tweets further and allow them to show

up on those feeds.

This means users would find sponsored tweets from companies mixed in the stream of tweets

from their followers.

This makes the ads more intrusive and could harm the user experience, said Ryan Knapp, who

relies on Twitter for social reasons and to promote his business, Buffalo Futsal, a form of

indoor soccer played five-on-five with a heavier ball.

Twitter needs to be careful because, unlike Facebook, its members haven&#8217t stored the

photos, videos and other key components of their online lives on the site, he said.

&#8220In the end, it is a tool, and people can decide to leave or start using it in a

different way&#8221 that sidesteps the ads, Knapp said.

The Associated Press contributed to this report.