If you want to target the young, it might be advisable to publish online. The music industry has heard the sound of MP3 and it is changing its tune. Even I thought I might read more if I bought a Rocket eBook Reader and tried reading with its larger fonts. Maybe SF is more appealing on a futuristic gadget. Or maybe computers have so intruded in our lives and consumed our time, that unless something appears on a computer screen, it won't get noticed.
Young people do like to read because they like the Internet, and it is essentially a written medium.
The last theory believes that the magazines are failing because the stories are not entertaining. I have a friend who is an old timer like myself who grew up with the SF magazines and still subscribes to them. She tries to read each issue, but for the most part, thinks the stories are bad, poorly written, not entertaining, or deals with subject matter that is unappealing. She wants entertainment, writing with a lot of vivid description, and positive moods. If you look at the stats, Analog is by far the most successful of the magazines, and the most old fashion.