Dreaming of strangers and not knowing their identities are common. It represents the fact that you are seeking to explore outside your routines whether that involves engaging in lovemaking or breaking out from the normal dating.
In general, encountering a mysterious stranger in a dream can signify uncertainty about what is going on, and how you feel about meeting people for the first time. A stranger in your dream can also signify unrequited love and desire for intimacy with others who are not part of your life at this moment in time.
These mysteries of not knowing the people you dream about helps to heighten the senses of intrigue, and leaves you wanting more.