1. Ask some of your contacts who share the same surname
2. Do a Google search
3. Check on Facebook to see if there is a group with your surname.
4. Contact a local Historical Society or Library in the area of your ancestor to see if they know about upcoming reunions, and if they don't know, ask if they will give you the name of their favorite most helpful genealogist's name.
5. See if the name appears in the Directory of Family Associations, as shown below. I noticed it is sold at Amazon, but you might be able to get it at your local library, like I did. The second photo is an example of a page. If you are interested, it's worth checking this book out.
And, if you do go to a reunion, don't forget to bring your business cards, they could be handmade or professionally printed, using your own photos. See mine HERE.