Your alumni magazine probably reaches more alumni more consistently than any other medium, so it's important that you use it to promote your Switchboard.
House ads and articles are both good ways to feature Switchboard.
Kenyon College regularly features Switchboard and its success stories in their alumni magazine, like in this article from February 2018 and this story that introduced the platform to the Kenyon community in 2015.
Reed College used a similar article to announce the official launch of its Switchboard in 2014.
St. Andrew's College announced their Switchboard in The Andrean (p55).
Pitzer's half-page ad is successful because it features a testimonial front and center. The screenshot, though, may be too small for readers to make out the details:
Antioch's full-page ad follows a similar design, though, again, the screenshot may be too small to make out the details. When using screenshots it may be more valuable to highlight a single post with comments rather than the entire homepage:
Santa Clara's small blurb made use of space left over by other elements on the page: