Post-Interview Thank You Note without contact information (need answer fast)

I just had a phone interview with two people, but I was not given either of their contact information. I’d like to send them thank-you notes. I can think of two ways to do this, and I’d like to know which is preferable:
[ol]
[li] Send the note to the recruiter (whose address I have), asking for it to be forwarded to the interviewers, or[/li][li] Send the notes through LinkedIn contact requests, with the invitation to continue the conversation at the end.[/li][/ol]
Which one should I choose?

My personal opinion is that if the interviewer doesn’t offer any sort of contact info then they do not expect a thank-you note, and probably prefer to keep some distance and let the recruiter handle all follow-up communication. So option #1 is the better one but really, I don’t think it’s necessary for a phone screen.

FWIW we just finished a round of interviews and my boss thinks it’s weird when someone looks her up on linkedin after a phone interview. I haven’t had it happen but can’t say I’d feel differently. (That said, recruiters seem to love to add anyone and everyone. I assume because it grows the network they can mine for leads.)

I do lots of phone screens, and don’t expect thank you notes - it is not like it is a big hassle. Did you get feedback? I usually phone screen with someone, and it is pretty clear by the end of it whether we are going to recommend an invitation.
If you get one, then research the company and combine a thank you note with a specific question showing you’ve done your homework.
I give people who’ve done their homework a lot more brownie points than people who send thank you notes. But none of it counts as much as knowing your stuff and showing high energy during the interview.

It was a second round interview, not just a phone screen. We discussed some technical information, and I’ve thought of some additional things they might be interested in after the interview. However, the company hasn’t given out their emails overall—we’ve been communicating through a third-party job posting site. Given that, I think it’s a better bet to send everything to the recruiter, and hope that it gets forwarded.

You mention sending LinkedIn requests, so I assume this means you at least have their full names? If so, poke around the company website a bit until you find an email address for somebody at the company, anybody, and use that email naming convention to send your emails directly to your interviewers.