There is always risk of losing money in the stock market. And all stocks are different - some are riskier than others. A multi-billion corporation is far more established and stable than a new startup just entering the market. So before you invest anything, you must know your investment goals, time horizon, and risk tolerance.
The good news for you is that since you're 17, you have a lot of time - and the more time you have, the more risk you can take on, since there is time to recover in case of a downturn. If you think long term, avoid the Big Money Fast hype, diversify, and make good choices, you can make a ton of money for your retirement. When you look back over the last 90 years, even through the Great Depression and Bush Recessions, 2 out of 3 years stocks went up.
Try taking this investor questionaire to see what kind of investor you are:
https://personal.vanguard.com/us/FundsInvQuestionnaire
Above all, Follow the traditional time tested advice:
Have a goal - know what you are investing for, and choose the right investment to achieve it.
Choose the right amount of risk - neither too cautious nor too reckless.
Do your research - choose what's right for you - not someone else, especially a sales rep.
Be diversified and allocate your investments properly.
Think long term and avoid the Big Money Fast hype.
Don't invest according to emotion - especially greed, fear or panic.
Don't just look at the investment - consider fees/taxes/commissions around it.
Start with some basic books to teach you the fundamentals. Three excellent books are The Complete Idiot's Guide to Investing, Investing for Dummies, and Mutual Funds for Dummies. You can probably find them in your local library.