In our society, very poor examples are often set regarding relationships between men and women. Many in our society view premarital sex as "normal." As such, unmarried couples engage in the intimate activity that should be reserved for marriage. This includes passionate kissing and foreplay. This type of kissing and touching more often than not leads to intercourse. Of course, this is contrary to God's teaching. In 1 Corinthians 6:18 it says, "Flee sexual immorality. Every sin that a man does is outside the body, but he who commits sexual immorality sins against his own body." Clearly, in this verse, the apostle Paul is warning against the kind of intimate kissing and touching that can lead to sexual intercourse.
When it comes to dating, we encourage teenagers to not get romantically involved with someone of the opposite sex or have a "steady" boyfriend or girlfriend. Group dating and general social contact is much better for teens than pairing off with a specific individual. It is our general advice that one-on-one dating be reserved for the time people are ready (in respect to age, education and finances) to get married. In any event, the kind of passionate kissing and petting that you asked about should be reserved for marriage, where they can help build the special, intimate bond God designed.
For more information on this subject, read "A Touchy Subject: Hand-holding, Hugging, Kissing and More . . ." by David Treybig, which appeared in the Jan.-March 2004 Vertical Thought. You may also want to read "Sex, Dating and You" by Tom Clark, which appeared in an edition of Youth United.