A prerequisite for the damsel in distress is likely attractiveness. Multiple studies have shown a majority of white men exclude black women as dating options, with almost half describing themselves as having rare or zero attraction to black women. All races were shown to find underweight or average-weight women more attractive. Obesity is approximately 20% more prevalent in black women vs white women. If the majority of a population is white, and these stories are fueled in large part by what people find beautiful and therefore place a higher value upon, it's likely part of the equation. We understand missing men regardless of the race does not garner much media attention. Is that explained by sexism? I am not convinced the explanation for "Missing white women syndrome" is racist media or society. I do think if Gabby Petito was hideously ugly, we wouldn't be talking about it. I also do not think the findings mentioned above are solely the result of racist white people. For example, black male faces are considered more attractive than white male faces. Black female faces are considered least attractive by all races. A possible explanation is lower perceived femininity, as this is known to correlate with lower attractiveness ratings of female faces.
A recent review of "MWWS" states physical attractiveness was not factored into any previous analysis. It's listed among a small group of potential factors that need to be included along with socioeconomic status and the potential for white women to be victims of crimes that feature unique or newsworthy characteristics. For example, living in a van in the middle of nowhere, eating vegetables with a jealous and controlling boyfriend. Most importantly, there are limitations in the data "MWWS" is based upon. An overview:
Zach Sommers, Missing White Woman Syndrome: An Empirical Analysis of Race and Gender Disparities in Online News Coverage of Missing Persons, 106 J. Crim. L. & Criminology (2016).