We consider the Threshold Activation Problem (TAP): given social network $G$ and positive threshold $T$, find a minimum-size seed set $A$ that can trigger expected activation of at least $T$. We introduce the first scalable, parallelizable algorithm with performance guarantee for TAP suitable for datasets with millions of nodes and edges; we exploit the bicriteria nature of solutions to TAP to allow the user to control the running time versus accuracy of our algorithm through a parameter $α\in (0,1)$: given $η> 0$, with probability $1 - η$ our algorithm returns a solution $A$ with expected activation greater than $T - 2 αT$, and the size of the solution $A$ is within factor $1 + 4 αT + \log ( T )$ of the optimal size. The algorithm runs in time $O \left( α^{-2}\log \left( n / η\right) (n + m) |A| \right)$, where $n$, $m$, refer to the number of nodes, edges in the network. The performance guarantee holds for the general triggering model of internal influence and also incorporates external influence, provided a certain condition is met on the cost-effectivity of seed selection.