Some of the best online sites for finding an intimate partner are listed in the adult personals section of this website.  If you are seeking to find your partner online, and that is a pretty safe way to go about it and stay out of your work and friend circle, you shoud try these resources:

The best two are:

adultfriendfinder.com
ashleymadison.com

Others to try:

marriedsecrets.com
discreetadventures.com

Online is not the only way to find someone, but it's the most anonymous and easy to try without risk.

I really hated adultfriendfinder.com.  As a woman, I found myself overwhelmed by solicitations from men to such an extent that I could not keep up with all of the emails I got.  I also found that the sheer size of the site and the truly overwhelming number of just nasty human beings made it an unpleasant experience within a very short period of time.

I met a few men on there, whom I believed I had properly screened, only to find out that they lied about just about everything, just to get my attention, which they promptly lost as soon as I discovered their glaring lies.  Most of the lies related to age and personality.  I quickly learned that due to the intense competition for attention there, lies were probably necessary.

All of that said, many women I know have had success on adultfriendfinder.com, but they also have way more time than I do to weed through the responses and to meet potential candidates.  If you have limited time, it will probably be overwhelming.

I used Craig's List briefly and got burned a couple times.  I then found Adult Friend Finder and was overwhelmed, but found a gem that I am over the moon with!