I know not all celebrities are good, they take drugs, swear, etc. But just because a few of them are like that doesn't mean we should generalize and say that they shouldn't. Some people look up to celebrities that help charity, support same sex marriage ( eg. Angelina Jolie ), help orphanages, etc.
Meriam-Webster defines celebrities as "a person who is famous". These are some of the most well-known businesspeople, politicians, scientists and so on. People become famous by working hard at their goals and the fame tends to be connected to fortune. So in that sense, being inspired by Britney Spears is horrific, but being inspired by the likes of Steve Jobs is a wonderful thing. Having a mentor, both in-person and in popular culture can each give some form of auditing for lessons.
Celebrities should not be regarded as role models for teenagers. In a perfect world, everyone who is "celebrated" would be a wonderful role model. But our celebrities are not! So many celebrities engage in irresponsible behavior that is deemed entertaining--drug use, promiscuity, and unhealthy lifestyles. Unfortunately, teenagers are still going to look up to celebrities. But it is our responsibility, as the adults in their lives, to show them what it really means to be a good person.
In a traditional moral view, no human is a good role model, other than Jesus, if he existed. Celebrities are only people who have done whatever they could to become popular. In most cases, they have broken many moral rules in doing so, and still break them to keep their fame. I'm not saying that celebrities are worse than the general public, I'm simply saying that they aren't morally good.
Everywhere on the news, there are new reports of celebrity scandals. They take drugs, wear inappropriate clothing, and do many other bad things. Besides, celebrities do very little good for others and are not happy themselves. Look at all the celebs who committed suicide (Robin Williams). They appear happy to us but deep down, they're not. Instead of these celebrities, we should be looking up to scientists and innovators, or people who actually help others and make a difference in the world.