user7039: Can Metta be practiced in a partnership or as a team? 
I can think of

two people practicing Metta together, or 
a group which meets for meditation, or 
across borders, across continents people meditate together at a certain time.

Are there any indications of a Sutta?
Are there practices of a tradition?

user-1: Yes there is a mentioning, the famous sutta, its starts out with hints of being withdrawn from the world like "not overly attached to families" and is actually not meant as a social event. But since "sex" sells it is broadly sold like that, introduced like that. If one just likes to maintain pleasant feeling, one can go on an thinks this way, but if one has certain metta (maybe for the living beings that would lose there lives to be able to meet in a beloved group) and like to put his practice also in line with metta, this first lines of the Suttas become to have reasons.
There is a nice summary of all qualities required to practice metta and its really not an ordinary mans task and so is it with the benefits one would gain, of which you would just gain sort time pleasure if its made for simply some personal pleasure.
Karaṇīya Metta-Sutta - The Message of Peace and Universal Friendliness, by Ven. Ñāṇadassana Maha Thera.
And to your question if there are such metta-events and practices, actually 95% are of such as you have thought of.
One might also consider the question and answer here in: Metta and Loving-Kindness as a Team
See also: Metta Means Goodwill (Thanissaro Bhikkhu). At least metta is not meant to get involved, but more a beneficial kind of thought for others for one who is actually on leave or on a journey, leaving for a good with the thought "Sabbe sattā sukhī attānaṃ pariharantu." "May all living beings look after themselves with ease." (The Sublime Attitudes | audio)
So where do you like to go?
(Note: this answer has not been given with the agreement to be means of trade or the purpose of/for trade and/or keep people trapped and bound. How you handle it lies in your sphere, but does not excuse the deed here either.)

user7141: You are allowed to practice as a team. In fact in Lord Buddha's time and even now people and Monks do it. But the important thing is to use this good friendship as a boat and use the excitement of teamwork to your benefit. 
Remember not to be too attached to the team. You will be more willing to meditate when yo got friends around. 
Even Lord Buddha said

Good friends (Kalyana mitta) are the strength of Buddhism

But never discuss your meditation with your friends, Because it will awake each others ego and that would do more harm than good. But if you have any issues with your practice seek the help of a good master. I would advice you to seek a kind monk because ordinary people can be a bit ego driven.

user295: Meditation influences the surrounding by vibration created. (You can really feel the vibration when you experience Piti) So when you pratice as a group these vibrations influence others, especially when you are having a bad patch in meditation then the influence of others will help in to develop calmness and concentration and perhaps dispel agitation and other hindrances that might have surfaced during your worldly interactions.
This is true for all types of meditation but most effective when doing Metta as vibrations tend to be stronger.

7039: <p>Can Metta be practiced in a partnership or as a team? </p>

<p>I can think of</p>

<ul>
<li>two people practicing Metta together, or </li>
<li>a group which meets for meditation, or </li>
<li>across borders, across continents people meditate together at a certain time.</li>
</ul>

<p>Are there any indications of a Sutta?</p>

<p>Are there practices of a tradition?</p>
 -1: <p>Yes there is a mentioning, the famous sutta, its starts out with hints of being withdrawn from the world like "not overly attached to families" and is actually not meant as a social event. But since "sex" sells it is broadly sold like that, introduced like that. If one just likes to maintain pleasant feeling, one can go on an thinks this way, but if one has certain metta (maybe for the living beings that would lose there lives to be able to meet in a beloved group) and like to put his practice also in line with metta, this first lines of the Suttas become to have reasons.</p>

<p>There is a nice summary of all qualities required to practice metta and its really not an ordinary mans task and so is it with the benefits one would gain, of which you would just gain sort time pleasure if its made for simply some personal pleasure.</p>

<p><a href="http://zugangzureinsicht.org/html/tipitaka/an/an03/an03.099.than_en.html" rel="nofollow noreferrer">Karaṇīya Metta-Sutta - The Message of Peace and Universal Friendliness</a>, by Ven. Ñāṇadassana Maha Thera.</p>

<p>And to your question if there are such metta-events and practices, actually 95% are of such as you have thought of.</p>

<p>One might also consider the question and answer here in: <a href="https://buddhism.stackexchange.com/questions/13154/metta-and-loving-kindness-as-a-team">Metta and Loving-Kindness as a Team</a></p>

<p>See also: <a href="http://zugangzureinsicht.org/html/lib/authors/nanadassana/metta_en.html" rel="nofollow noreferrer">Metta Means Goodwill</a> (Thanissaro Bhikkhu). At least metta is not meant to get involved, but more a beneficial kind of thought for others for one who is actually on leave or on a journey, leaving for a good with the thought "<em>Sabbe sattā sukhī attānaṃ pariharantu.</em>" "May all living beings look after themselves with ease." (<a href="http://zugangzureinsicht.org/html/lib/authors/dhammayut/chanting_en.html#sublime" rel="nofollow noreferrer">The Sublime Attitudes</a> | <a href="http://sangham.net/index.php?action=tpmod;dl=get197" rel="nofollow noreferrer">audio</a>)</p>

<p>So where do you like to go?</p>

<p><em>(Note: this answer has not been given with the agreement to be means of trade or the purpose of/for trade and/or keep people trapped and bound. How you handle it lies in your sphere, but does not excuse the deed here either.)</em></p>
 7141: <p>You are allowed to practice as a team. In fact in Lord Buddha's time and even now people and Monks do it. But the important thing is to use this good friendship as a boat and use the excitement of teamwork to your benefit. </p>

<p>Remember not to be too attached to the team. You will be more willing to meditate when yo got friends around. </p>

<p>Even Lord Buddha said</p>

<blockquote>
  <p>Good friends (Kalyana mitta) are the strength of Buddhism</p>
</blockquote>

<p>But never discuss your meditation with your friends, Because it will awake each others ego and that would do more harm than good. But if you have any issues with your practice seek the help of a good master. I would advice you to seek a kind monk because ordinary people can be a bit ego driven.</p>
 295: <p>Meditation influences the surrounding by vibration created. (You can really feel the vibration when you experience <a href="https://en.wikipedia.org/wiki/P%C4%ABti" rel="nofollow">Piti</a>) So when you pratice as a group these vibrations influence others, especially when you are having a bad patch in meditation then the influence of others will help in to develop calmness and concentration and perhaps dispel agitation and other hindrances that might have surfaced during your worldly interactions.</p>

<p>This is true for all types of meditation but most effective when doing Metta as vibrations tend to be stronger.</p>
