Is it possible for a virgin to get pregnant if pre-ejaculated liquid came on her string during humping?

Pregnant?: From your description, it is highly unlikely that you will become pregnant from someone having placed pre-ejaculate fluid on your tampon's string.

Doubtful: Is the string attached to a tampon? A tampon would act as a barrier to sperm. Pre-ejaculate may contain large amounts of viable sperm (less common), smaller amounts of sperm that are dead or alive or no sperm. There is potential for pregnancy with pre-ejaculate. Sperm need to be deposited in vagina or at introitus for pregnancy to occur. Use protection every time.