I have had success reaching out to those who I suspect have a somewhat solid connection to my own family through some documentation I may have received from IKG-Wien about one of my family relations who lived in Vienna around the time of WWII, as well as through some information I might have found on Geni.com, JewishGen, or MyHeritage.com.  I have written both e-mails and snail mail, and have been quite successful for the most part in finding distant relatives of mine. 
In all cases when I contacted potential relatives I always laid out exactly how I suspected that we were related.  In 20+ years of research I have only had two rejections from people I knew were related to my family.  I suspected that they thought I wanted something more than just to share information with them or else did not want to have any contact with me for other personal reasons even after I outlined how I was sure that we were related.

The one that was most interesting turned out to be another family of one of my great-grandfathers that I knew nothing about.  She lives in Israel and was delighted to hear from me.  She knew nothing about the birth of my grandmother so I added to her tree as well as adding another branch of the family to my own tree.  She even sent me pictures of my great-grandfather (that I did not previously have), as well as her whole family tree.  So now it appears that my grandmother's birth might have been out of wedlock.  I was able to actually meet another cousin related to a sister of one of my grandfathers who I previously never knew existed.  In this case I wrote both snail mail and e-mail. Through JewishGen's Family Finder I had someone actually contact me from Australia asking about information regarding my paternal grandfather.  This resulted in my finding information about two brothers of my grandfather I previously was not aware even existed - which resulted in my locating relatives from this family in various places around the world that I keep in touch with via e-mail and Facebook. 

So my advice to you is don't get discouraged and don't give up!.

Joyce Eastman
wildwoman@...