I am unaware of any strain that is used purposefully to enhance libido nor has been proven to. In fact this use is entirely subjective and actually quite ridiculous, Kratom's primary uses are pain and Depression relieving - so its possible Kratom through its psychological effects can 'subjectively' boost libido but because of its effects on general mood. I've heard many claims about aphrodisiac effects but they don't seem to be substantiated and there is always a question of spiking of the herbal ingredient.

Ganesh MD and Gold MD may be valid strains for this use but again - there is question as to the WHY these strains would behave in that way. Drawing questions of standardization practices and contamination concerns. 

It is probably best to just stick with a company that produces exceptionally potent strains in general, such as TopExtracts & Coastline Kratom. ;)