As I was doing an online construction executive job seeker search, I noticed a co-workers resume on the net. He is a valued construction executive and one that I don\'t want to loose. Should I leave it alone or talk to him about it?

Please do not overreact. There are times when professionals will put their resumes on the net for possible bites. He may be very happy in his position with your construction employer but wants to see what other professionals in the industry are making.
First, I would meet with this person to discuss job satisfaction. There may be other reasons for the posting as well. It could be a need to relocate, maybe moving closer to family, being closer to home or ability to telecommute.
Keep the lines of communication open with this construction executive and invite him to come and speak to you at any time with concerns or problems. I would not bring up the fact that you have viewed his resume nor would I tell anyone else in the office.