Teenagers may experment with oral sex and outercourse as ways to be sexual with their partners that preserve their virginity and avoid exposure to the risk of pregnancy. They may also simply enjoy these activities as relatively low-risk ways to explore their sexuality -- even within an established sexual relationship. Thus, it is important for teens (and adults!) to understand that although these types of sex are relatively safe, they are not completely without risk.
Dry humping, and other forms of body rubbing can pass on diseases that spread by skin-to-skin contact, such as herpes and genital warts, and oral sex can also pass on these diseases, as well as those that spread via bodily fluids.
Becoming aware of the risks of various forms of sexual expression, even the minor ones, can help people make informed decisions about their sexual lives. Before having sex, or even fooling around with someone, it's always a good idea to talk about previous sexual experiences and exposures. Testing may also be a good choice, and people can also practice safe oral sex to reduce its risks, or use barriers to make dry humping safer.
Maintaining your virginity, if you define that as avoiding vaginal intercourse, is a relatively effective method of avoiding pregnancy -- and possibly evading parental or religious censure. However, if you engage in other sexual activities, you can still be exposed to other sexual risks, whether or not you are still, technically, a virgin.
Note:The widespread lack of understanding of these topics may be, in part, attributable to the many sex education programs that focus on virginity instead of comprehensive sex education. These programs can leave young people not only uninformed about the risks and pleasures of sexual activities other than vaginal intercourse but without the tools they need to make good decisions about sex and otherwise keep themselves safe.
