The following is an example of ride sharing that the FAA illustrates as being acceptable. The Washington State West Sound  Pilots Association is endeavoring to form a pilot’s on-line bulletin board type of access for aviation enthusiasts to share in flights. These flights could be proximate to the base airport, or trips of various lengths and distances. The group is designing an app that can be used by the members to post flight ideas for others to join in. The requirement under  § 61.113(c) that there be nothing more than a pro-rata share of the expenses will be strictly followed. Are there any concerns that you, my fellow pilots foresee? Do you like the idea? Should it pass FAA scrutiny? Any & all feedback much appreciated from AOPA & AOPA-member visionaries! We'd love to see our little experiment proliferate, should it be permissible. 

FAA Example

1: 22 A private pilot wants to post a note with the specific time and date she is traveling to Long Island on a fixed-base operator (FBO) bulletin board in order to carry two additional passengers in exchange for pro rata reimbursement of expenses under § 61.113(c). Such advertisement on a bulletin board may be acceptable, as long as it targets a limited and defined audience as discussed in paragraph 10.2.1 above.

4 Replies
If you're going to open it to all "aviation enthusiasts", it wouldn't be legal.  See Flytenow v. FAA, decided in 2017  And that USCA ruling stands since the US Supreme Court declined last year to hear Flytenow's appeal.  See also the FAA's 2019 letter on offering ride sharing on the internet.  Basically, if members of your group want to privately share rides among members, that would probably fly.  But the instant you go beyond your association's membership, it's not going to pass FAA muster.  And opening up your association's membership to the general public rather than just pilots in the West Sound area would also make it illegal.
Thanks to pilot Ronald Levy for the inciteful commentary. I will narrow my description of the general concept and fly it by you and the community again. 
Ros Stovall
I was hoping more to provide insight rather than to incite anything, but if you carefully read the FAA's letter you may be able to figure out how to do this within your association without holding out to the public.  But if you read between the lines, I think you'll see the FAA really doesn't like this.
Ron---thanks for your insightful feedback on the "Ride Share" app concept.
Our group is meeting tonight (4/18/2020) and I'd like to be able to provide good guidance.
I'd love to toss some scenarios around with you. Call, text or email your availablity:
Ros Stovall (317) 502 1950. rosstovall@gmail.com.