Penny stocks are very risky. You need to realize that almost all penny stocks are shell companies, and that they basically have no real value. I dabbled in penny stocks in my early investing career, but learned quickly that they aren't the right choice if you want to make money in the long term. Penny stocks are also plagued with pumpers and dumpers (probably the ads you've seen are by pumpers).
If you don't know much about trading penny stocks, I'd be very cautious to start getting into that. Be very careful, you can lose money just as quickly as you can make it with penny stocks.
I actually wrote an article on my blog about the risks of penny stocks if you're interested in more information.
Click here for the article.