Personal Ads for Cabin Mate ???

A friend of mine, is looking to go on a cruise this year, but is single and doesn't want to pay the double rate. I understand Cruise Critic does not allow requests for Cabin Mates..... which leaves me wondering if there are other reputable places, that are cruise specific for this type of search.

there is one competing web site that allows this, plus a group not quite as good on facebook.