Gunnermann Family of New York

[Karl E. Gansberg]

After the 1900 census, it appears that my Gunnermann Family has completely disappeared from any ancestry.com records.  Checking GGG records and Find-a-grave nationwide draws a complete blank.  I could see maybe a couple of people disappearing, but a whole family with 7 children vanishing.  I've heard that many German families change their surnames, especially during the WW1 era.  Anyone have any ideas/suggestions.  I've even tried different spelling of the surname.

[John Reynolds]

Are you searching Fred J. (age 39 in 1900), with wife Mary(age 38)of 167 W 31st St NYC ?
Children Fred Jr, (age 17), Charles (age15), Henry (age 13) etc.