You could try a "widget" on the lawyer's site which facilitates getting generic questions answered for free.

The idea being that in each practice area, there might be a handful of questions that they get asked frequently, and would commit to answering one-time. It could be used to qualify the web visitor (always a good thing) while satisfying the visitor by providing them an answer. Of course, the challenge here is that most lawyers might only be comfortable providing such watered-down generic advice, that the answers themselves wouldn't be very useful. But this way, you could provide value to lawyers somewhat comfortable with online discourse, while building up content. With enough lawyers and content, you could then expand the service to build towards your larger vision.

But as John has mentioned, many entrepreneurs have and are actively trying to win with this type of idea and have often struggled. CaseText is a recent YC grad that is doing some interesting work in this area.

Happy to talk through your product implementation.

Look to history - there are lots of legal services that have tried this and failed. What did they do or not do?

Unfortunately, you can't always turn something into a viral marketplace. IMHO there are too many built-in disincentives in the legal world to create the kind of viral loops you're looking for.

I would recommend you a blog post from The Family, a great French Accelerator, on this topic. They give you many advices on 2-side markets :

http://blog.thefamily.co/post/67650035686/koudetat-hacking-2-sided-marketplaces

There's certainly many things you can try for customer acquisition -- SEO, ads, partnerships, creative marketing campaigns, etc. In regards to those that are specifically referrals, I think clients can refer lawyers, and vice versa.. especially if you offer some tool / workflow that makes that relationship (once created) a much better experience.

This is how you do it:
You launch with ONLY one legal specialty, like real estate law for example. You share equity with 5 real estate lawyers, one who mostly handles closings, one who mostly handles landlord/tenant court and so on. Pick their brains individually, for the "easy money" questions they are routinely asked by their existing clients and the most routine services provided to their existing clients and become a high level expert in their respective areas.

Their involvement and your commitment to understanding their business is the first step towards getting your new equity partners to generate your content. For example your new partner that focuses on landlord/tenant court will reveal to you that when a landlord has a non paying tenant, that landlord usually notifies your partner after the delinquent tenant hasn't paid for 75 days, so his challenge is setting expectations for the landlord.
Then he/she will reveal that the first step is for your new partner to assess the landlord's situation and level of documentation/correspondence, followed by a 3-day rent demand letter, a summons and complaint and depending on the circumstances a court date within 45 days in either landlord/tenant court or Supreme Court. And then your new partner has to explain to his landlord client that a judgment is only as valuable as the ability to collect funds, meaning the tenant may not have enough assets to cover the delinquent amount owed. Then of course landlords can get blind sided as tenants fight for a "partial constructive eviction," which is essentially when the tenant says "Hey I would have paid my rent, but the heat was off or the toilets didn't work, so I wasn't able to conduct business, therefor I am entitled to reduced rent."
That is exactly how NYC Real Estate Law works right now and understanding the minutia is key b/c you need to share this information to be perceived as an expert.
You can offer lawyers and their clients meaningful value by analyzing what is being done currently, how it can be improved, but most importantly for right now: How it can be illustrated so you and your lawyer partners can be viewed as the experts you are; This is a great opportunity to illustrate these processes/systems using infographics, so if you don't have a designer, get one. Inform landlords how things work and they will appreciate it immensely, b/c it makes for more accurate reporting and conversations with their partners, more accurate financial projections etc.

Showing people how things work gets them involved and loyal, so I hope this helps.

Btw, who cares about other services that look similar on paper and failed, you are going to be dynamic and offer truly meaningful value and that always wins...

All the best,
Gregg M. Kennelly

For a double-sided marketplace, I recommend doing the following:

1. Pick a niche service specialty. If you're just starting out, determine which service speciality can get you the most early traction through secondary research. Make sure your basic premise (macro-level thesis) is solid.
2. Create your customer persona
3. Validate that by speaking with 30 prospects (or a statistically significant sample size).
4. Pivot (if need be)
5. Build your supply and create liquidity
6. Generate transactions and ...

I can go on about this, but I'm sure it will be never ending. Happy to talk more about this, if it would help.