Welcome to those of you coming to Dreamwidth from Tumblr. I have found a few communities that may help you connect with people here.
the_great_tumblr_purge is especially for people moving to Dreamwidth so you can find folks you knew on Tumblr.
tumblrmigration has some resources on how to make the move effectively and get the hang of DW.
Friending communities help you find new people:
addme covers everything.
addme_fandom is for all fandoms.
startrek_add_me is for fans of the Star Trek mythos.
add_a_writer connects writers with other writers, and gives readers a place to find new writers to follow.
If you were using Tumblr for inspiration and need a replacement muse, consider:
allbingo supports any kind of creative bingo. A new thematic fest appears each month. You can play a public card, make your own, or use one from an outside event.
crowdfunding is for creators and consumers of cyberfunded creativity. Watch for the mid-month Creative Jam where you can leave or claim prompts.
If you miss the pretty pictures, try:
shutterspeed offers photography prompts.
picture_prompt_fun invites people to write stories from pictures.
photocons posts icons made from photographs. Get some 100x100 user icons here!
solitude_in_sight has photos without people.
drawesome is a fanart community.
artists is a community for art creators and lovers.
graphics is an all-purpose visual art community.
If you wish to copy this list, or use it as inspiration to make you own, by all means do so. Helping Tumblr refugees feel more welcome, and making communities more active, will benefit everyone.