Finding and identifying your ancestors is not always straight forward. You may know where you ancestor was or should be but when you check the local records, they aren't there. However, they may be someone else who looks familiar but has a different name.
One thing you will find as you get deeper into your research is that names can change. There may be good reasons for the change or you may never know why they change, but change they do.
In order to identify your ancestor you need to build an identity for them. You need to record names, places, dates, relationships, activities and characteristics.
Relationships can be one of the most helpful things. Know who lives with your ancestors and who lives nearby. People often move in groups and this can help you to recognize when your ancestor has changed their name.
Try not to get ahead of yourself. Gather as much information as you can about the last known location where you are certain you have the correct ancestor.
Gather as many documents as you can. Try not to rely on only one source for any facts. Use records like death records to gather information but always be aware that they are not a primary source.
Once you have your ancestor surrounded by family, friends and neighbors you will be in a better position to follow them back to their previous location.
Use the census to see who was living in the same community with your ancestor and also who was in the house. Never assume relationships. A child living with a family may not be their child, it can be a relative, neighbor or an orphan.
Try to avoid going on a fishing expedition, be systematic in your research.