See sources below

See sources below

Social pressure messages are roughly an order of magnitude more influential than conventional [...] appeals
— Prof. Donald Green, Columbia University
Social influence may be the best way to increase voter turnout
— Prof. James Fowler, UC-San Diego
The more personal the mode of contact, the more effective it is [at increasing turnout]
— Prof. Alan Gerber, Yale University
Voters are more likely to take an action if they’ve been compelled to do so by their friends
— Teddy Goff, lead digital strategist for Clinton and Obama campaigns

Academic research

Neighbor-to-neighbor encouragements to vote delivered via canvassing boost turnout by 9.0 percentage points (Middleton & Green, 2008)

Friend-to-friend encouragements to vote delivered via Facebook boost turnout by 8.2 percentage points (Teresi & Michelson, 2015)

When volunteers discuss voting with one member of a household, the probability of other members of that household’s voting increases by 5.8 percentage points because “interpersonal influence shapes the behaviors of people living within the same household” (Nickerson, 2008)

 

Chart Data Sources
Effect size of mail, phone calls, and canvassing:
Green, Donald P., Mary C. McGrath, and Peter M. Aronow. "Field experiments and the study of voter turnout." Journal of Elections, Public Opinion & Parties 23.1 (2013): 27-48.

Effect size of GOTV messages delivered by friends:
Teresi, Holly, and Melissa R. Michelson. "Wired to mobilize: The effect of social networking messages on voter turnout." The Social Science Journal 52.2 (2015): 195-204.

Middleton, Joel A., and Donald P. Green. "Do Community-Based Voter Mobilization Campaigns Work Even in Battleground States? Evaluating the Effectiveness of MoveOn’s 2004 Outreach Campaign." Quarterly Journal of Political Science 3 (2008): 63-82.