18%-43% of reported forced marriages in the UK involve male victims.

Study conducted by the FMU.

Data from Karma Nirvana.

Considering 65% of reported cases involved adults, I'm going to suggest that the prevalence of male victims of FM is on the 43% end of the spectrum. Why? Such unions are generally forced upon both unwilling participants by both families.

Even in cases involving children and teenagers, there has been little done to consider adults, in these arrangements, potential victims as well. Now there are probably plenty of scumbags, or just a completely different cultural understanding of marriage and statutory rape, but the latter is significantly less relevant in the West.