Daily proportion of @-mentioned users which are located within a tag city.

<p>Noise is eliminated by smoothing with a 4.</p

Targeted social mobilization in a global manhunt

Social mobilization, the ability to mobilize large numbers of people via social networks to achieve highly distributed tasks, has received significant attention in recent times. This growing capability, facilitated by modern communication technology, is highly relevant to endeavors which require the search for individuals that possess rare information or skills, such as finding medical doctors during disasters, or searching for missing people. An open question remains, as to whether in time-critical situations, people are able to recruit in a targeted manner, or whether they resort to so-called blind search, recruiting as many acquaintances as possible via broadcast communication. To explore this question, we examine data from our recent success in the U.S. State department's Tag Challenge, which required locating andphotographing 5 target persons in 5 different cities in the United States and Europe { in under 12 hours { based only on a single mug-shot. We find that people are able to consistently route information in a targeted fashion even under increasing time pressure. We derive an analytical model for social-media fueled global mobilization and use it to quantify the extent to which people were targeting their peers during recruitment. Our model estimates that approximately 1 in 3 messages were of targeted fashion during the most time-sensitive period of the challenge. This is a novel observation at such shorttemporal scales, and calls for opportunities for devising viral incentive schemes that provide distance or time-sensitive rewards to approach the target geography more rapidly. This observation of '12 hours of separation' between individuals has applications in multiple areas from emergency preparedness, topolitical mobilization

Daily number of impressions on Facebook for the winning team CrowdscannerHQ, and the official Tag Challenge organizers.

<p>The vertical dotted line denotes the release of the first mug shots.</p

Distance convergence toward Tag Challenge cities of web hits on http://www.tag-challenge.com.

<p>We consider a moving average of distance filtered daily tweet traffic (MA(prop(t))) (grey circles), which is fit with a linear regression (red line) giving a correlation of .</p

The total daily number of Tweets (black line), the number targeting individuals via @-mentions (blue line) and their proportion (red line).

<p>Correlation of targeted proportion with time was found as .</p

Map showing communication network within Europe and North America following an unbiased random walk (upper) and under 30% targeting (lower).

<p>The area of red circles are proportional to centrality.</p

Daily volumes of Tag Challenge related Tweets and Web hits on http://www.tag-challenge.com up to the challenge day. Major media coverage events are highlighted.

<p>Daily volumes of Tag Challenge related Tweets and Web hits on <a href="http://www.tag-challenge.com" target="_blank">http://www.tag-challenge.com</a> up to the challenge day. Major media coverage events are highlighted.</p

Plot of stationary distribution during a random walk on global MSA network, with increasing degree of greediness (targeting) moving clockwise from top left.

<p>The red line represents an pure, untargeted random walk, corresponding to pure random mobilization via broadcast messaging. (Top left) The horizontal dashed line represents the uniform distribution of centralities expected in a fully connected graph. The black line in other plots represents a greedy random walk. (Bottom right) When the greediness is increased to we match the observed proportion of targeted messages reaching the Tag Challenge cities. The shading represents MSAs from different continents. The 5 tag cities are marked with vertical, dashed blue lines.</p

Daily proportion of @-mentioned users which are located within a tag city.

<p>Noise is eliminated by smoothing with a 4.</p