Twitter is preparing to open up its site to advertising, according to All Things Digital. The site reports that the immensely popular social media site, which processes more than 50 million messages per day, is working on an ad model similar to that of Google where ads would appear on the site based on user searches. Of Google’s $24 billion of revenue, 97% comes from advertising. All Things Digital reports that the ads will only show up in search results and will not be a part of a user’s Twitterstream. The launch of the ad platform could happen before July.