As more and more advertising dollars flow into social media, some Madison Avenue firms are seeking to grab a piece of the action. But it will be a tough fight as the space is overrun with companies seeking to own the segment, from start-ups to public-relations firms.

Universal McCann, the media-buying firm owned by Interpublic Group of Cos., is bolstering its social-media offering by launching a practice this week called Rally. The division will help marketers develop campaigns, track online chatter about their brands and measure how those campaigns perform. Headed by Heidi Browning, a former MySpace executive, Rally will house several new social-media hires. MySpace, like The Wall Street Journal, is owned by News Corp.