There is no need to cite this package when used. You may want to (read and) cite the article on Amelia, the software whose model this software adopts and adapts.

James Honaker, Gary King, Matthew Blackwell (2011). Amelia II: A Program for Missing Data. Journal of Statistical Software, 45(7), 1-47. URL http://www.jstatsoft.org/v45/i07/.

Corresponding BibTeX entry:

  @Article{,
    title = {{Amelia II}: A Program for Missing Data},
    author = {James Honaker and Gary King and Matthew Blackwell},
    journal = {Journal of Statistical Software},
    year = {2011},
    volume = {45},
    number = {7},
    pages = {1--47},
    url = {http://www.jstatsoft.org/v45/i07/},
  }