Piperazines are a pretty large family of compounds with effects that are still being teased out. It is likely that the family will yield a compound that would generate the exact effects that you're looking for, but as of yet, the family is likely still pretty young for someone to be able to provide a reasonable recommendation that isn't overly subjective - a recommended piperazine likely wouldn't be generalizable to multiple individuals.
Finding a sustainable social 'lubricant' is one of the holy grails of neuroscience - imagine how marketable and lucrative a healthy, mood lifting drug would be. Every middle-class family would have their children on it as fast as you can say 'my child is an honor student.' Compounds that are known to be social 'lubricants' for a majority of individuals are stimulants such as amphetamine and cocaine, which both induce social behavior in a cross-species manner. Other compounds have had social benefits attributed to them too, however. Short-acting benzodiazepines such as alprazolam have been highly effective for some individuals for this effect. Another class would be the opioid compounds found in pharmaceuticals such as hydrocodone, oxycodone, or other synthetic opiates such as demerol or tramadol. Tramadol is a special synthetic opiate due to the fact that it also has SSNRI activity as well, which many of SWIM's cohorts have considered to be helpful in social interaction.
Nootropics such as the racetams or phenibut, as well as supplements such as R-alpha lipoic acid, yohimbine, or good 'ol caffeine have also yielded some nice social lubricants.
The bottom line, however, is that no one has found the perfect compound that is widely generalizable to enough individuals. When someone does, you wont be able to avoid commercials for the drug. Try phenibut - many people consider it to be FAR too sedating (swim would fall into this category), while many others consider it to be one of the best sustainable supplements to induce a sense of well-being. A few friends enjoy combining phenibut with caffeine to enhance social interaction at parties.