• by Laurie Sullivan  @lauriesullivan, June 1, 2011

Twitter has begun to roll out search features and a new photo-sharing service. The search tool should give users easy access to more relevant Tweets when searching for something or clicking on a trending topic. It also will show related photos and videos. When logged in using the new Firefox browser, the latest version will let users type a hashtag or @username into the address bar and go to a search results page or profile page.

During the next several weeks, Twitter also will release a way to upload a photo and attach it to tweets from Twitter.com. Users will soon be able to do this from its official mobile apps. Photobucket will host the photos, and Twitter will continue to allow users to use third-party services, such as Twitpic and Yfrog.

Twitter wants to encourage developers to build out apps for the site. There are more than 600,000 developers who have downloaded 900,000 API keys, and there are thousands of Twitter clients. At the All Things Digital D9 conference Wednesday, Twitter CEO Dick Costolo said the site gets 13 billion API requests daily. Mobile use rose 150% since January. The site processes 1 billion tweets every six days; the first billion took three years.

Also, advertisers gain a high rate of return. The Volvo ad had a 50% engagement rate, according to Costolo. Twitter supports about 600 advertisers, up from 150 at the end of 2010.

Research from the Pew Internet & American Life Project finds that 13% of adults who use the Internet have used Twitter as of May 2011, up from 8% in November 2010. The majority are college graduates between the ages of 18 and 49, and bring home an annual income of between $30,000 and $49,999, or more than $75,000. Fifty-four percent of those participating in the survey access Twitter via mobile phones.

Twitter adoption rose among non-Caucasians. In fact, one in 10 African-American Internet users visit Twitter daily -- double the rate for Latinos and nearly four times the rate for Caucasians. The study also found significant growth among 25-34 users. Between November 2010 and May 2011, Twitter use more than doubled from 9% to 19%. Twitter use among those 35-44 rose from 8% in late 2010 to 14% in spring 2011, compared with the youngest adults ages 18 to 24, who were the most likely to use the service in Pew's first survey.

On Tuesday, Twitter introduced the Follow button, which allows users to discover and instantly follow Twitter accounts directly from the Web sites, rather than signing on to Twitter. More than 50 publishers and Web sites have added the button. AOL, bnet.com, CBS News, MarketWatch, Sports Illustrated and Vanity Fair are among the first Web sites to include Twitter's Follow button.

Google followed up on Wednesday by rolling out the +1 share button to all search results and ads. The button will begin appearing on sites across the Internet, especially Best Buy, Nordstrom, Bloomberg and Rotten Tomatoes. Users will also see the button on Google properties such as Android Market, Blogger, Product Search and YouTube.