I've found Find a Grave can be a little frustrating when I'm searching for someone whose last name could be spelled in various ways, or if the person in question has married and I'm not sure of the correct spelling of her married name. They can be a little persnickety about spelling, and you can't search by the deceased's first name alone, which with well over one million burials isn't really feasible anyway. There is a back door however, if you have an idea where the burial may have taken place.
Select "Search for a cemetery" on the home page. Now you can select a specific state and county. At this point, a list of cemeteries will appear which you can whittle down further by village or town. Once you have selected a cemetery, you will be able to search by first name alone. Granted this works best in smaller cemeteries or if the first name is an unusual one like say, Wentworth, but if you've been unable to find the burial the traditional way it may be worth a try.