Multivariate testing is a popular method to improve the effectiveness of digital marketing in industry. Online campaigns are often conducted across multiple platforms, such as desktops, tablets, smart phones, and smart watches. We propose minimum sliced aberration designs to accommodate online experiments with four platforms. This approach provides important insights into how different sets of design factors work differently across the four platforms, which can be used by industry for optimizing many forms of digital marketing. The effectiveness of the proposed approach is illustrated by an industrial email campaign with four platforms.