Digital marketing company ValueClick Inc. announced Wednesday that John Giuliani will become the firm’s new chief executive. Giuliani, who has been the company’s chief operating officer since April, will replace James Zarley, who in turn has been named executive chairman of the Westlake Village firm’s board of directors. “This is the perfect time to expand John’s role, considering the company’s momentum under his leadership,” said Zarley, in a prepared statement. “His early success in bringing our assets together has shown he has the expertise and experience to lead ValueClick through its next phase of growth.” The company is one of the largest Internet-based marketing companies, specializing in email, display and mobile marketing through several subsidiary brands. Giuliani was chief executive of Dotomi Inc. of Chicago when it was acquired by ValueClick in 2011. He was previously president of the North America division of Catalina Marketing Inc. in St. Petersburg, Fla. “I am excited to accept the chief executive role, as our integration efforts to date reinforce the fantastic opportunity we have to become a differentiated leader in digital marketing,” Giuliani said in a statement. On Wednesday, shares of ValueClick closed up 34 cents, or nearly 1.8 percent, to close at 19.12 on the Nasdaq.