* James Zarley to replace Tom Vadnais as CEO
* Sees Q1 rev at mid point of prior forecast
* Shares down 6 pct after market (Adds details; updates share movement)
April 9 (Reuters) - Online advertising firm ValueClick Inc VCLK.O said Chief Executive Tom Vadnais was stepping down and will be replaced by predecessor and Executive Chairman James Zarley, effective immediately.
Zarley, an angel investor in ValueClick, served as its chairman and CEO from 1999 -- a year after its founding -- to 2007.
Vadnais took over as CEO from Zarley in May 2007. Since then, ValueClick shares have lost about two-thirds of their value.
Zarley will be succeeded by director Martin Hart as executive chairman, the company said in a statement.
Vadnais, who is retiring, will act as a consultant to Zarley for the remainder of 2010, the company said.
The company also announced that it now expects first-quarter revenue at the mid-point of its prior forecast of $93 million to $97 million.
Analysts on average were expecting revenue of $97.9 million, according to Thomson Reuters I/B/E/S.
ValueClick, which owns brands such as Commission Junction, Smarter.com, CouponMountain.com and PriceRunner, expects adjusted EBITDA to be at or slightly above the high-end of the previous outlook of $24 million to $26 million.
Shares of the Westlake Village, California-based company were down 6 percent in after-hours trading, after closing at $10.05 Friday on Nasdaq. (Reporting by Gowri Jayakumar in Bangalore; Editing by Unnikrishnan Nair, Anthony Kurian)