To cite rtweet use:

Kearney MW (2019). “rtweet: Collecting and analyzing Twitter data.” Journal of Open Source Software, 4(42), 1829. doi:10.21105/joss.01829, R package version 0.7.0, https://joss.theoj.org/papers/10.21105/joss.01829.

Corresponding BibTeX entry:

  @Article{rtweet-package,
    title = {rtweet: Collecting and analyzing Twitter data},
    author = {Michael W. Kearney},
    year = {2019},
    note = {R package version 0.7.0},
    journal = {Journal of Open Source Software},
    volume = {4},
    number = {42},
    pages = {1829},
    doi = {10.21105/joss.01829},
    url = {https://joss.theoj.org/papers/10.21105/joss.01829},
  }