Not really sure what to say, but serotonin is the love hormon and together with a psychoactive drug and euphoria you should be set to go.
Serotonin can be acomplished with MDAI, and you may enforce euphoria by adding Ethylphenidate later into the trip. I heard different ideas on making the perfect "horny" pill, however it depends a little from person to person I believe. 4-aco-mipt is considered by some as the mipt of choice for making people horny, while others say 5-meo-mipt (hey, did you people even try 4-aco-mipt?).
Once we had some 2c-b/2c-t-x'ish ecstasy pills, theese for some reason made a girl super horny. To bad we never knew the mix in theese pills, I am guessing there were larger doses of 2c-e in them than advertised.
In short I would say all compunds that messes with 5-HT reseptor will make people very confortable and horny. A magic pill that could boost a dopamine rush for 30 minutes then slide into serotonin and then euphoric state Im thinking will do it. Not that hard to do really, we are living in times of designer drugs.
2C-D also gets people horny, because of the phenetylamines and therefor delicious bodyload you get from it (unless you get visuals on top), so again different people different strokes.
I do not think there is ONE compund alone that makes you horny and will do the trick - it is always combinations of 1+ compunds, atmosphere, good music and connection. Unless you would like to drug someone into heaven and rape them - which is sick twisted and not allowed when playing with people's head.'
Our moral compass needs to be on track here!