The acquisition will allow small businesses to "create, schedule, manage, and measure their social media marketing campaigns" on Facebook and Twitter, Vertical Response said in a statement.
Roost's services also will make it easier for users to "build and manage engaging customer relationships." The company offers pre-fab campaigns for a range of industries that can serve as conversation starters for customers on Facebook and Twitter.
The number of VerticalResponse customers sharing e-mail marketing campaigns with their social networks increased over 1,400 percent in the past year, according to CEO and founder Janine Popick. The company's flagship product is its bulk e-mail delivery service.
Vertical Response, founded in 2001 and profitable since 2005, has grown 150 percent in the past three years. The San Francisco-based company has nearly 100 employees.
Popick told Information Week she discussed a partnership with Roost but that buying the company made more sense.
"We concluded this could be really core to our offerings, and we needed to take it one step beyond a partnership," she said.
Said Roost CEO Alex Chang: "We realized we were servicing a lot of the same companies with the same kind of products." Roost's website now reads, "Roost by VerticalResponse."
Roost services are free for now, though the four-year-old company, also based in San Francisco, has plans to introduce add-on services that will cost $10 to $40 per month. That will still happen, though the timing is unclear.