Consider the surname Snider, or maybe Snyder or Snijder. And it may have originally been spelled with some additional consonants so it looked like Schneider. Families may have shortened a long surname, Americanized it, or even varied the spelling for other reasons. Spelling wasn't as standardized in times past as it is now. Additionally, many people were illiterate and when they needed to spell something, they spelled it the way it sounded. This means each and every person, including your ancestor may have had a different interpretation of how their surname was spelled.
So how do you find someone whose name seems to change every time they write it? How do you even figure out what the variations are?
• Think like a 3rd grader. One way to figure out some possible variations is to get help from someone who sounds everything out phonetically: a 3rd grader. Ask your child, grandchild, or borrowed neighborhood children how they would spell a certain name. You may be surprised at some of the ways they think it is spelled. Kids don't have our adult brain that tells us that a certain spelling is wrong. They can guess all the possibilities without editing it in their minds. If you don't have a child handy to help you, just sit down with a piece of paper and start playing with ideas about how a surname could have been spelled. Consider different vowel combination and extra consonants that may have been thrown in.
• Try using wildcards to catch additional spellings of a surname. Most search engines provide for a wildcard. The wildcard allows you to substitute a symbol (usually an asterisk *) for one or more letters in a word. In Ancestry, you can type in the first three letters of a first name or a surname and then place an asterisk (*). This will help you add more results than just typing the name as you "know" it should be spelled. An example would be my surname of Philibert. When searching in Ancestry you could type in Phi*, this could help you to get hits that would spell my surname as Philbert or Philabert. In using the wildcard for a first name it may help in picking up different versions of a first name like Mar* would look for Maria, Mary, Marie, Marisol, etc. One way you can use a wildcard when you search Google is by placing a wildcard in the middle of the name like John * Jones. This tells Google that you want to find results that may include something in the middle of John and Jones such an initial or a middle name.
• Consider the way a surname could have been indexed. Many problems exist when you take a document and ask people (or even computers) to index them. One problem that can come up is how the person interprets the last name. I've seen times when a surname prefixed with Van is indexed with Van as a middle name. So the surname is indexed as only the part that comes after Van. This can also happen with names that start with Mc or Mac. This is why it's important to be open to lots of ways a name could be interpreted, not just when it was originally written but years later when it is indexed into a genealogical database.
• If a Soundex search is available, use it. A Soundex feature allows you to search surnames that sound like the surname that you are searching. This is especially helpful in looking through lists where a surname might be spelled a number of ways. Soundex doesn't rely on how the name is spelled, it's a system that codes names based on how they sound. In the case of Johnson, it doesn't matter whether it is spelled Johnsen, Johnson, or Johnsan, you will be able to find it. When using Ancestry, for example, you can choose to search a name using "Exact" spelling or "Soundex." While the exact spelling may narrow result, it may also rule out instances where a person's name was misspelled.
• A handy online tool that may be of use to you is the Table of Common Surname Variations and Surname Misspelling. This website, which specializes in Canadian genealogy, provides a list that contains 10,500 surname spelling variations.