SWIFT

unrecognized font family Helvetica-Regular

// put this in app delegate to discover the correct namo 
// of the font you are searching

for (NSString* family in [UIFont familyNames])
{
    NSLog(@"%@", family);

    for (NSString* name in [UIFont fontNamesForFamilyName: family])
    {
        NSLog(@"Family name:  %@", name);
    }
}