Please read everything about dating 
(Answer to Question #1 above above)  which applies here too.  (click
here for that). The Arabic word used in the Quran &
Hadith is "zina". In Arabic, zina applies to both
unmarried and married people.  (Zina includes ANY sex
outside of marriage.)  Therefore pre-martial sex is
strictly prohibited just like adultery.

Quran 017.032  "And come not near unto adultery. Lo!
it is an abomination and an evil way."

Beware also of ANYTHING leading to illegal sexual
relations since this too is a sin and a type of zina
and haram. Things that lead to haram are haram by
principals of fiqh.

The eyes commit adultery, the tongue commits adultery,
the hands commit
adultery, the feet commit adultery and then the
private parts confirm it or deny it." (Musnad Ahmad
bin Hanbal, Hadith no. 8488.)

Illegal sexual relations is a MAJOR SIN in Islam.
Do not go near this.

Stay away from zina and the things that lead to it:
(1) Bad company (2) Wrong movies and tv programs, etc.
(3) Haram internet (4) Bad books

Increase the things that help you increase your iman
(belief): (1) righteous
company (2) salat (3) sawm (fasting) (4) sadaqa (5)
join or start a halaqa group for learning Islam and
meeting the right people.

And Allah(swt) knows best.