AllOver Media, the Plymouth-based firm that sells nontraditional advertising opportunities at gas pumps, ice lockers and restrooms was sold Friday to a private equity firm that will help finance an aggressive expansion plan.

Terms of the sale between AllOver and Boston-based Audax Group were not revealed.

AllOver CEO Tony Jacobson called the transaction "a nice deal" and said the existing executive team will remain in place and business will continue as normal.

Jacobson said the 13-year-old company, with 135 employees, hopes to quadruple its presence in the nontraditional outdoor advertising segment over the next five years, both organically and through acquisition.

AllOver had about $40 million in revenue last year with 1,700 clients in the U.S. and Canada.

"We have a list of 40 companies that we want to look at," Jacobson said in an interview. "There are a lot of regional companies out there and companies with 10 or fewer employees."

In the past two years, AllOver has made seven small acquisitions, which helped it grow from a $6 million company less than a decade ago.

"Out of home" advertising, a segment that runs from billboards to transit advertising, rose to $7 billion in 2014, according to the Outdoor Advertising Association of America. The "alternative" category, in which AllOver competes, accounted for $855 million in sales.

AllOver used the Minneapolis investment banking firm Greene Holcomb & Fisher to search for a buyer.

Omar Akbar, a vice president with the investment bank, said there was "strong" interest among private equity firms in the advertising company.

"What makes AllOver attractive is that they have nationwide scale and reach in the alternative out-of-home market," he said. "They also have the opportunity to expand in the static [print] and digital category."

Jacobson said Audax, which specializes in lower-middle capital companies, was the acquirer of choice.

"These guys are not operations guys; they are a data company," he said.

Audax co-CEO Geoffrey Rehnert said AllOver has an "unparalleled reputation for providing innovative advertising products and exceptional service."