11. The computer program product of claim 7 , the computer program product further comprising the program code executable by the processor to: determine a first set for subset selection, the first set including a portion of the strangers on the social network; rank the first set based on the fitness scores; compute a value of an optimization objective function for each of intervals in the first set; determine an interval in the first set, the interval in the first set having an optimal value of the optimization objective function; determine a second set for selecting the one or more of the strangers for the information spreading; rank the second set based on the fitness score; and program instructions to determine an interval in the second set, the interval in the second set being defined by the interval in the first set, based on percentiles.
7. A computer program product for selecting strangers for information spreading on a social network, the computer program product comprising a computer readable storage medium having program code embodied therewith, the program code executable by a processor to: train statistical models with history data of the information spreading of strangers on the social network, the strangers on the social network being not known to a requester who requests the strangers on the social network to conduct the information spreading; compute information spreading probabilities based on features of the strangers on the social network; compute information reach of the strangers on the social network; compute information spreading probabilities based on a wait time of the strangers on the social network, the wait time being a period of time for the strangers on the social network to initiate information spreading in response to being requested by the requester; compute fitness scores of the strangers on the social network, the fitness scores being a function of the information spreading probabilities based on features, the information reach, and the information spreading probabilities based on the wait time; rank the strangers on the social network in a sorted set, based on the fitness scores; select one or more of the strangers for the information spreading from the sorted set; and wherein the one or more of the strangers for the information spreading are selected by determining an interval in the sorted set, the interval satisfies an optimization objective of minimizing time for the information spreading within a confidence probability.