Shares in ValueClick Inc. lost ground for the second straight day after it was downgraded by Piper Jaffray & Co. due to concerns over a Federal Trade Commission probe into its sales practices.

The Westlake Village-based online ad brokerage firm had seen shares surge 30 percent in the past week due to rumors the nation’s second-largest Internet ad firm was a buyout target.

The FTC inquiry is focused on the company’s lead-generation business, which accounted for more than 60 percent of the company’s first quarter sales. The FTC said it is examining the company’s use of e-mail and free gifts.

Shares in ValueClick were down 54 cents to $32.09 in afternoon trading on the Nasdaq.